Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue crack propagation under the condition where the superimposed stress history with different
frequency components given intermittently,
TAKAKI Yoshifumi and GOTOH Koji,
Quarterly Journal of The Japan Welding Society, Vol.38, No.1, pp.19-24, 2020.

DOI： https://doi.org/10.2207/qjjws.38.19

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes the application of weight function for stress intensity factor in a surface crack with a wide range of crack shapes.
Based on the weight function representation proposed by Wang and Glinka (2009), an extended formulation of the weight function for surfaces and embedded cracks is performed.
The unknown parameters in the formulations were determined from reference values of stress intensity factor for a surface and an embedded crack given by finite element analysis with the J integral method.
The effectiveness of the proposed weight functions has been verified by comparing with the stress intensity factors given by finite element analysis and available approximated solutions under several loading conditions.

DOI： https://doi.org/10.1016/j.marstruc.2019.102696

Repository Public URL： http://hdl.handle.net/2324/4751320

Language：Japanese   Publishing type：Research paper (scientific journal)  

Numerical Simulation of Fatigue Surface Crack Propagation under In-plane Biaxial Cyclic Loading with Different Phases,
Mizuki Morishita, Yosuke Anai, Shuichi Tsumura, Koji Gotoh and Toshio Niwa,
Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol.30, December 2019, pp.115-121.

Repository Public URL： http://hdl.handle.net/2324/4794743

Language：English   Publishing type：Research paper (international conference proceedings)  

The application of advanced welding technologies is important for improving the efficiency of hull construction processes and reducing production costs.
Laser-arc hybrid welding technology, which combines the advantages of laser and normal arc welding, is of high quality and is expected to improve productivity.
The Japan Ship Technology Research Association has organized the joint industry project in collaboration with a university, a classification society and some shipyards to apply this technology in the construction of general merchant ships, in which the plate thickness of the main structural member is thicker than passenger ships and high speed craft.
The overview of the first phase JIP results were introduced in PRADS 2016. In this presentation, an overview of main research results of the second and third phase JIP, which are listed below, are introduced.

DOI： https://doi.org/10.1007/978-981-15-4680-8

Repository Public URL： http://hdl.handle.net/2324/4752585

Language：English   Publishing type：Research paper (international conference proceedings)  

Floating wind turbine facilities installed in deep sea areas play an essential role in the promotion of green energy.
One of the problems associated with the commercialization of facilities installed in the deep sea is the maintenance cost of mooring chains, because they are expensive and wear between links leads to chain breakage. Therefore, it is necessary to establish a quantitative wear evaluation method for mooring chains.
An experimental facility to reproduce the wear caused by sliding between links at the scale of an actual floating wind turbine was developed to investigate the wear performance in seawater conditions, and wear tests were conducted.
Substitute ocean water was applied to the experiment instead of seawater.
In addition, a procedure for nonlinear finite element analysis was improved to estimate the behaviour of wear between links.
Measured stress versus strain relations of the links was considered in the finite element analysis.
The experiments and numerical analysis confirmed that the amount of wear in the substitute ocean water was less than that obtained in dry air and that the tensile force between links is an important factor for the degree of wear between links.

Repository Public URL： http://hdl.handle.net/2324/4753064

Language：English   Publishing type：Research paper (international conference proceedings)  

Floating wind turbine facilities, which are installed in the deep sea area, plays an essential role to promote the green energy application.
One of the problems associated with the commercialization of facilities installed in the deep sea is the reduction of the maintenance cost of mooring chain, because breaking of the mooring chain caused by the wear between links leads to enormous economic losses.
Therefore, it is necessary to establish a quantitative wear evaluation method for mooring chains.
Experimental facility to reproduce the wear caused by sliding between links in actual scale applied for floating wind turbine, which had been proposed by the authors, was updated and the wear tests was conducted by setting some tensile force conditions between the links.
Besides, procedure of the nonlinear finite element analysis was improved to estimate the behaviour of wearing between links.
From experiments and numerical analysis, it has been confirmed that the tensile force between links is an important factor of the wear amount between links.

Repository Public URL： http://hdl.handle.net/2324/4753060

Language：English   Publishing type：Research paper (scientific journal)  

The reducing effect of the angular distortion in T-type full penetrated welded joints fabricated by laser-arc hybrid welding was investigated. The angular distortion caused by the laser-arc hybrid welding were measured and compared with one caused by CO2 gas shielded-arc welding. As a result, the amount of angular distortion by laser-arc hybrid welding was the same level as one in the case of forming a leg size of F1 grade regulated by the Common Structural Rules for Bulk Carriers by applying arc welding. In addition, numerical analysis of the welding deformation was carried out by thermal elastic–plastic finite element analysis and these results were generally consistent with the measured results. Moreover, the effect on the FE result of the penetrated shape is discussed.

DOI： https://doi.org/10.1080/09507116.2016.1223234

Language：English   Publishing type：Research paper (international conference proceedings)  

To produce offshore wind power generation plants, deep-sea floating wind turbine facilities are required. Commercial installation of floating wind turbine facilities requires a reduction of the mooring cost. Mooring chain breaks due to progressive wear will lead to enormous damages. Therefore, a quantitative wear evaluation method for mooring chains needs to be established. In this study, an experimental setup was constructed to reproduce the wearing phenomenon in mooring chains due to the motion of the floating body induced by waves, and its usefulness was confirmed. The result of the wear test conducted in this study suggests that the tensile force between links affects the degree of wear. Additionally, numerical simulations were performed using a finite element model with measured wear characteristics of the link material to reproduce the phenomenon of wear between links and confirmed that the wear phenomenon could be represented by numerical simulation.

Repository Public URL： http://hdl.handle.net/2324/4753059

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Overview of a joint industrial project for introducing laser-arc hybrid welding to the construction of general merchant ships in Japan.
Koji GOTOH,Tsutomu FUKUI,Atsuo MORIYAMA,Shuichi TSUMURA and Hiroshi SAWATO
Proceedings of 13th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2016), ID 014, September, 2016.

Repository Public URL： http://hdl.handle.net/2324/4794457

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Effect of compressive residual stress on fatigue crack propagation.
Yasushi MORIKAGE, Satoshi IGI, Tetsuya TAGAWA,Kenji OI,Koji MURAKAMI and Koji GOTOH.
Proceedings of 13th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2016), September, 2016.

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4753057

Language：Japanese   Publishing type：Research paper (scientific journal)  

Kohei YAMASHITA and Koji GOTOH,
Numerical simulation of fatigue crack propagation with crack opening and closing based on the strip yield model considering the strain hardening effect of materials,
Journal of the Japan Society of Naval Architects and Ocean Engineers,
Vol.21, June 2015, pp.31-42

Repository Public URL： http://hdl.handle.net/2324/4794431

Language：English   Publishing type：Research paper (international conference proceedings)  

Fatigue life estimation for planar cracks, e.g. part-through surface cracks or embedded cracks is very important because most of fatigue cracks found in welded built-up structures show planar crack morphologies.
Although authors had proposed the estimation procedure of crack shape evolution for a planar crack based on the fracture mechanics approach, this method cannot apply if the values of stress intensity factor at the vertices of the surface crack approximated as an ellipse cannot calculated.
Then, development of the shape evolution procedure of a planer crack under the stress field with arbitrary gradient, because fatigue cracks in welded built-up structures exist near the stress
concentrated region.
A Practical estimation formula the shape evolution of a surface crack under stress field with the gradient is proposed in this study.
This formula is established by considering the stress field under no crack condition and some former proposed formulae under uniform and pure bending stress fields.
The validity of the proposed formula are confirmed by comparing some measured surface crack shape evolutions under some stress gradient conditions.

Repository Public URL： http://hdl.handle.net/2324/4793204

Language：English   Publishing type：Research paper (international conference proceedings)  

Overview of the quantitative evaluation procedure of strain rate and temperature effects on fracture toughness proposed by the authors is introduced.
Important concept of former researches is that the fracture toughness is a function of the strain rate-temperature parameter (R), which enables to unify both strain rate and temperature effects for the mechanical properties of materials.
Using this knowledge, the equivalent temperature shift values at arbitrary strain rate from static loading condition are proposed.

Repository Public URL： http://hdl.handle.net/2324/4793205

Language：English   Publishing type：Research paper (scientific journal)  

Fatigue crack propagation under the biaxial tensile loading, which loading directions are normal and parallel to the initial crack position, is highlighted in this study.
Most of in-service structures and vessels are subjected to many types of loading.
Generally, these loadings have different axial components with different phases.
However, the structural integrities of structures and vessels are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition.
Most of these codes are based on the S-N curves approach.
An approach that does not use S-N curves has been favored by researchers, with the fracture mechanics approach preferred for evaluating the fatigue life of structures.
An advanced fracture mechanics approach was developed based on the Re-tensile Plastic zone Generating (RPG) stress criterion for fatigue crack propagation.
In this study, fatigue crack propagation tests under biaxial loading with six different phase and loading conditions are performed and the effect of the phase difference under biaxial loading is evaluated.
A numerical simulation method of fatigue crack propagation based on the RPG stress criterion under different biaxial loading phase conditions is presented and compared to measured data.

DOI： http://dx.doi.org/10.1016/j.marstruc.2015.03.003

Repository Public URL： http://hdl.handle.net/2324/4751319

Language：Japanese   Publishing type：Research paper (other academic)  

Koji GOTOH, Shuich TSUMURA and Issei UCHINO;
Overview of the joint research project for introducing laser-arc hybrid welding in Japanese shipbuilding industries,
Proceedings of the 82nd Laser Materials Processing Conference, January 2015, pp.83-39.

Language：English   Publishing type：Research paper (scientific journal)  

Fatigue crack propagation behavior under superimposed stress histories containing different frequency components with several mean stress conditions was investigated.
Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Re-tensile Plastic zone Generating) stress criterion for
fatigue crack propagation was improved to extract the effective part from the applied stress history for fatigue crack propagation.
The parameter, which is based on the plastic hysteresis energy consumed in the vicinity of a crack tip, was applied and implemented into the numerical simulation code of fatigue crack propagation.
Fatigue crack propagation tests under various superimposed stress conditions with several mean stress conditions were performed and compared with the fatigue crack propagation histories obtained from the improved numerical simulations.
These comparisons show the validity of the proposed procedure for extracting the effective stress history from the superimposed stress histories with different frequency components and mean stresses.
Additionally, practical fatigue strength evaluations based on the linear cumulative fatigue damage parameter were conducted to investigate the tendency of the fatigue damage value under these stress conditions.

DOI： http://dx.doi.org/10.1016/j.marstruc.2014.12.005

Repository Public URL： http://hdl.handle.net/2324/4751318

Language：Japanese   Publishing type：Research paper (scientific journal)  

Kazuki, Matsuda, Koji Murakami and Koji Gotoh;
Numerical Simulation of Fatigue Crack Propagation under Superimposed Stress Histories with Several Constant and
Variable Mean Stresses,
Journal of the Japan Society of Naval Architects and Ocean Engineers,
Vol.20, 2014, pp.131-137.

Language：English   Publishing type：Research paper (international conference proceedings)  

Numerical simulations of fatigue crack growth of welded structural component were performed under fatigue testing conditions with block loading and constant stress range and the fatigue crack growth profiles were measured under the same loading conditions. In the experiments, fatigue cracks developed at the boxing fillet welded toe and grew toward the top flange plates of the specimens.
An advanced fracture mechanics approach based on the improved effective stress intensity factor range, which is the RPG (Re-tensile Plastic zone Generating) stress criterion, was applied to perform the numerical simulations of fatigue crack growth in the modeled components. A comparison of estimated fatigue crack growth profiles with measured ones verified that a reasonable estimation of fatigue crack growth can be estimated by applying the proposed numerical method.

Language：English   Publishing type：Research paper (international conference proceedings)  

Most of in-service welded built-up structures, which contain many welded joints as fatigue crack initiation sites, are subjected to many types of loading and these loadings have different axial components with different phases.
However, the structural integrities are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition.
Most of these codes are based on the S-N curves approach.
On the other hand, authors proposed the numerical simulation method of fatigue crack propagation histories of a cracked plate subjected biaxial loadings with phase difference of each loading component.
Fracture mechanics approach is applied to establish our method. In this study, fatigue crack growth behaviour of an out-of-plane gusset welded joint under biaxial loading with two different phase conditions were investigated.
The phase difference effect for fatigue crack shape evolution under biaxial loading was confirmed by measured ones.
Besides, comparisons of measured crack evolution with the numerical simulation results were performed to validate of our fatigue crack growth simulation for welded joints.

Other Link： http://www.sciencedirect.com/science/article/pii/S2211812814002491

Language：English   Publishing type：Research paper (international conference proceedings)  

Fatigue crack propagation behavior under simulated whipping loadings which contain two different frequency components is highlighted. Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Re-tensile Plastic zone Generating) stress criterion for fatigue crack propagation is improved to enable the extraction of the effective loading history. The critical value of the plastic hysteresis for the stress versus strain relationship occurring in the vicinity of a crack tip is defined as the control parameter for extracting the effective loading history. Comparison of fatigue crack propagation curves obtained from the improved numerical simulations with the measurements which were conducted by Sumi (2010) is performed. These comparisons show the validity of the proposed procedure for extracting the effective loading history from the superposed loading history containing different frequencies. In addition, imperfection of the S-N curves approach, which corresponds to the combination of the linear cumulative damage law and the loading cycle count by the rain flow method, is conducted.

Language：English   Publishing type：Research paper (international conference proceedings)  

Fatigue crack propagation under biaxial tensile loading is highlighted in this study. Ships and offshore structures are subjected to many types of loading, e.g. wave induced forces, gravity, and inertia forces. Generally, these loadings have different axial components with different phases. However, the structural integrities of structures and vessels are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition. Most of these codes are based on the S-N curves approach. An approach that does not use S-N curves has been favored by researchers, with the fracture mechanics approach preferred for evaluating the fatigue life of structures. An advanced fracture mechanics approach was developed based on the Re-tensile Plastic zone Generating (RPG) stress criterion for fatigue crack propagation. In this study, fatigue crack propagation tests under biaxial loading with four different phase conditions are performed and the effect of the phase difference under biaxial loading is evaluated. A numerical simulation method of fatigue crack propagation based on the RPG stress criterion under different biaxial loading phase conditions is presented and compared to measured data.

Language：English   Publishing type：Research paper (international conference proceedings)  

Fatigue crack propagation behaviour under superposed loading histories which contain two different frequency components is highlighted.
Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Re-tensile Plastic zone Generating) load criterion for fatigue crack propagation is improved to enable the extraction of the effective loading history.
The critical value of the plastic hysteresis for the stress versus strain relationship occurring in the vicinity of a crack tip is defined as the control parameter for extracting the effective loading history.
Comparison of fatigue crack propagation curves, obtained from the improved numerical simulations, with the measurements under the superposed loading
histories, is performed.
These comparisons show the validity of the proposed procedure for extracting the effective loading history from the superposed loading history containing different frequencies.

Language：English   Publishing type：Research paper (international conference proceedings)  

This paper presents an improved numerical simulation procedure for fatigue crack growth based on the strip yield model with a weight function.
In the previous numerical model, one-dimensional bar elements plugged up the chink corresponding to the virtual crack opening displacement in the plastic zone to describe the crack wake over fatigue crack surfaces.
However, this numerical simulation method gives poor growth estimations under large variable loading histories, e.g. spike overloading.
It is possible that insufficient consideration of the strain hardening effect of materials leads to excess crack closure.
The authors develop the numerical simulation model of fatigue crack growth by considering the strain hardening effect of materials using the modified strip yield model.
Numerical simulations of fatigue crack growth under many types of loading are performed to investigate the validity of our new proposed model.
Comparison of proposed simulation results with previous results and with experimental measurements confirms the superiority of the proposed method.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Improvement of the Dugdale strip yield model considering the work hardening effect of materials,
Keisuke HARADA and Koji GOTOH
Journal of the Japan Society of Naval Architects and Ocean Engineers,
Vol.14, pp.39-46.

Language：English   Publishing type：Research paper (scientific journal)  

Fatigue crack growht behaviour of A5083 series aluminium alloys and their welded joints,
Koji GOTOH, Koji MURAKAMI and Yasuo NODA,
Journal of Marine Science And Technology,Vol.16, No.3, 2011, pp.343-353

Repository Public URL： http://hdl.handle.net/2324/4785260

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4793203

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4794822

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4793199

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4795137

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4793206

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4793197

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Calculation Method of Crack Opening Displacement \\by Using Slice Synthesis Methodology And Strip Yield Model for An Embedded Elliptical Crack in Elastic-Perfect Plastic Bodies with Finite Plate Thickness,
Yukinobu NAGATA and Koji GOTOH,
Journal of the Japan Society of Naval Architects and Ocean Engineering, Vol.9, ,2009, pp.201-209

Other Link： http://www.jstage.jst.go.jp/article/jjasnaoe/9/0/9_201/_article

Language：Japanese   Publishing type：Research paper (scientific journal)  

Stress Intensity Factor and Crack Opening Displacement in Elastic Condition for Embedded Cracks
by Applying Slice Synthesis Methodology,
Yukinobu NAGATA and Koji GOTOH,
Journal of the Japan Society of Naval Architects and Ocean Engineering, Vol.9, ,2009, pp.191-199

Other Link： http://www.jstage.jst.go.jp/article/jjasnaoe/9/0/9_191/_article

Language：English   Publishing type：Research paper (scientific journal)  

Repository Public URL： http://hdl.handle.net/2324/4785261

Language：English   Publishing type：Research paper (international conference proceedings)  

Stress Intensity Factors for Three Dimensional Cracks by Applying Slice Synthesis Methodology
Koji GOTOH and Yukinobu NAGATA
The Proceedings of The Eighteenth (2008) International Offshore and Polar Engineering Conference

Repository Public URL： http://hdl.handle.net/2324/4793209

Language：English   Publishing type：Research paper (scientific journal)  

Repository Public URL： http://hdl.handle.net/2324/4793208

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4793200

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4785268

Language：Japanese   Publishing type：Research paper (scientific journal)  

Numerical Simulation of Fatigue Crack Initiation and Propagation for In-plane Gusset Welded Joints,

Language：English   Publishing type：Research paper (international conference proceedings)  

Physical Meaning of the Fictitious Crack Opening Displaecement in Dugdale Model

Repository Public URL： http://hdl.handle.net/2324/4795136

Language：English   Publishing type：Research paper (scientific journal)  

Repository Public URL： http://hdl.handle.net/2324/4785266

Language：Japanese   Publishing type：Research paper (other academic)  

A fatigue life prolonging method for welded built-up steel structures
by the grain fining around weld toe
Yukinobu NAGATA，Masahiro TOYOSADA，Koji GOTOH，Koji MURAKAMI
Proceedings of Welded Built-up Structures Integrity Symposium 2004, Japan Welding Society, pp.343-346

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4795134

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2003.12.005

Repository Public URL： http://hdl.handle.net/2324/4794800

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2003.12.006

Repository Public URL： http://hdl.handle.net/2324/4794799

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4752588

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4752584

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4752589

Language：Japanese   Publishing type：Research paper (scientific journal)  

Development of Evaluation Parameter for Fracture Toughness Based on Statistical Mechanics,
Journal of the Society of Naval Architects of Japan, Vol.190

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4752590

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4755283

Language：Japanese   Publishing type：Research paper (scientific journal)  

Evaluation of Brittle Fracture Accidents Occurred at the Hyogo-Ken Nanbu Earthquake,
Journals of the Japan Society of Civil Engineers, No.647 / I-51

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Study on Deformation due to Thermal Cutting,
Transactions of the West-Japan Society of Naval Architects, No.99

Language：English   Publishing type：Research paper (scientific journal)  

Repository Public URL： http://hdl.handle.net/2324/4753054

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4753056

Authorship：Last author   Language：Japanese   Publishing type：Research paper (other academic)  

Repository Public URL： https://hdl.handle.net/2324/7325943

Authorship：Last author   Language：Japanese   Publishing type：Research paper (other academic)  

Repository Public URL： https://hdl.handle.net/2324/7325945

Authorship：Last author   Language：Japanese   Publishing type：Research paper (other academic)  

Repository Public URL： https://hdl.handle.net/2324/7325944

Language：English   Publishing type：Research paper (international conference proceedings)  

Laser-arc hybrid welding (LAHW) can significantly reduce weld deformation due to the lower heat input compared to conventional arc welding, which is the standard method used in the current hull construction stages. Because of its superior heat concentration, LAHW has a relatively larger plate thicknesses over which I-shaped groove joints can be fabricated than conventional arc welding.
One of authors reported that one-pass welding without backing material was possible for a 17 mm thick steel plate with I-shaped groove. However, it was necessary to insert a filler gauge into the groove face and set the gap across the weld line to 0.5 mm.
From the viewpoint of introducing LAHW into the construction stage of general merchant ships, this study examined the welding work conditions to fabricate sound welded joints by LAHW under the following conditions: (1) groove fabrication by plasma cutting and (2) I-shaped groove with zero initial gap width. With reference to our previous studies, a search was conducted for welding parameters (laser power, arc current and voltage, etc.) that would allow the joint to be fabricated by a single pass of construction. As a result, although welding conditions with good bead appearance were identified, hot cracking of the weld metal occurred in some of the joints. To prevent hot cracking, the number of welding passes was changed from one to two, the length of the molten pool formed in the first pass was shortened in the thickness direction, and the second pass was performed by arc welding alone to compensate for the insufficient reinforcement height. As a result, it was possible to fabricate welded joints with good bead appearance without hot cracking.

Repository Public URL： https://hdl.handle.net/2324/7325691

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)  

This study explores the automation of welding inspection processes in shipyards by leveraging deep learning technologies to develop a system that aims to improve both efficiency and accuracy. We performed 90 horizontal fillet weld tests in a laboratory environment and 96 tests in a field environment on a T-shaped joint specimen, obtaining output logs from the welding machine during the welding process. We investigated deep learning computational methods and data preprocessing, introducing input data standardization and grid search for hyperparameters. As a result, the adjusted coefficient of determination for estimating leg length and undercut depth was improved. Next, we examined the frame size and the amount of frame shift for separating the input data were investigated, and the optimal values were identified that met practical criteria in a laboratory environment.
In addition, we conducted field tests using a simple welding carriage commonly used in shipyards to validate the applicability of our system in real-world environments. The results showed that the adjusted coefficients of determination for leg length and undercut depth estimation were 0.69 and 0.45, respectively, demonstrating the potential of our approach to improve production efficiency through automated weld quality inspection.
However, the study also identifies future challenges, including the need for more comprehensive training data, the incorporation of environmental data, and improvements in the estimation capabilities for various weld appearance features. This research serves as a step towards the automation of welding processes in the shipbuilding industry and provides directions for future research.

Repository Public URL： https://hdl.handle.net/2324/7337398

Language：English   Publishing type：Research paper (international conference proceedings)  

In the process of constructing the hull, additional anti-vibration measures are sometimes required during the commissioning phase after construction. However, the current process of installation involves welding, which results in paint burning and requires additional repair works to be painted. Therefore, the use of structural adhesives, which are a joining method that does not cause paint burning, is expected to replace welding.
In this study, as a basic study for the use of structural adhesives instead of welding for joining vibration isolation curling members, the joint strength under static three-point bending loading was compared with that of welded joints by experiments and finite element (FE) analysis. In these experiments, four types of specimens were prepared: an arc-welded joints (leg length of 5 mm) and three types of adhesives joints (adhesives thickness of 0.5 mm, 3 mm, and 5 mm) to not only compare welded joints with adhesives joints, but also to examine difference in strength due to the thickness of adhesives layer. The experimental results showed that all of the adhesives joints broke at lower loads than the arc-welded joints, but the adhesives joints also have sufficiently improved bending stiffness compared to the main plate alone and have not ruptured under the designed load. It was confirmed that the thinner the adhesives layer thickness, the greater bond strength. In the FE analysis, the interface region was defined in between steel and adhesives sections. It was confirmed that the elastic deformation before peeling could be simulated by applying appropriately material properties to each section. On the other hand, the adhesives modeling needs to be improved to estimate the peeling behavior and local strain distribution in vicinity of the adhesives part accurately.

Repository Public URL： https://hdl.handle.net/2324/7325690

Language：English   Publishing type：Research paper (international conference proceedings)  

It is known that fatigue crack growth behavior is dominated by cyclic plastic behavior near the crack tip. The purpose of this study is to improve the accuracy of measuring the dimensions of the alternating plastic region, which is the region where tensile and compressive plastic deformation overlap near the crack tip, using digital image correlation (DIC) method. To measure the dimensions of the alternating plastic region, fatigue crack propagation tests were conducted under two stress ratios using compact specimen (C(T) in ASTM E399). Two methods were employed to print speckle-patterns on the specimen surface for strain field measurement using the DIC method as analytical markers: (1) sprayed on the specimen surface with white and black ink, and (2) 3% nital etching solution was applied. To measure the alternating plastic zone (ῶ) under cyclic loading conditions, a high-speed camera was used to capture the strain fields near the crack tip under cyclic loading. To determine the dimensions of the alternating plastic zone, strain fields obtained from the results of the DIC method were analyzed. The elasto-plastic FE analysis was conducted to compare the results with DIC measurement. As the results, good agreement has been obtained in the low stress ratio condition rather than high stress ratio condition with the FE analysis.

Repository Public URL： https://hdl.handle.net/2324/7325689

Language：Japanese   Publishing type：Research paper (other academic)  

A study of the effects of laser irradiation and localized carburizing treatment on the fatigue strength improvement of welded joints.
Kazutaka TERATSUJI，Tomoya UCHIMURA，Koji GOTOH,
130-133

Repository Public URL： https://hdl.handle.net/2324/7160652

Language：Japanese   Publishing type：Research paper (other academic)  

Consideration on short crack propagation resistance in SM490 steels wiht different DKth
Yoshihiro HYODO, Masao YUGA, Yasuyuki KURIHARA, Thi-Huen Doan, Takahiro SAKIMOTO, Yoshiaki MURAKAMI, Tetsuya TAGAWA，Koji GOTOH,
163-167

Repository Public URL： https://hdl.handle.net/2324/7160653

Language：Japanese   Publishing type：Research paper (other academic)  

Basic Research on the Use of Structural Adhesives in Hull Construction.
Hiroyuki Onizuka, Shuichi Yamatoki, Koji Hifumi, Kazutomo Ito, Shohei Aramaki, Koji Gotoh, Koji Murakami, Toshiaki Iwata.
Conference Proceedings of JASNAOE, Vol.37, 2023, 2023A-GS21-3

Repository Public URL： https://hdl.handle.net/2324/7159846

Language：English   Publishing type：Research paper (scientific journal)  

Cyclic true stress - true strain curves were obtained using general-purpose shipbuilding steel in the large strain region. Test methods are incremental step test and static tensile test after cyclic loading.
The stress–strain curves for static and cyclic loading were compared to investigate the cause of the difference between each other.
A simple method for estimating the cyclic stress-strain curves was proposed.
The diameter and curvature of the smallest crosssection of the specimen were measured using telecentric measurement device, and the true stress - true strain curve was obtained using the Bridgman correction method.
Using the measurement method, cyclic stress-strain diagrams were obtained in the region where the true strain exceeded 1% by performing cyclic tensile tests using the incremental step method and static tensile tests after cyclic loading.
The influence of the test method and maximum displacement conditions on the cyclic stress-strain curve was small within the scope of this study.
There was little difference in the elongation between the static tensile test and the static tensile test after cyclic loading.
The difference in yield stress between static and cyclic loading was discussed in terms of macro-yield mechanisms at intergranular and transgranular.
A simple method for estimating cyclic stress-strain curves from a static stress-strain curve was proposed.
The specimens used in this study are general-purpose shipbuilding steels, and the results should be applicable to similar steels for welding and structures.

DOI： https://doi.org/10.1080/09507116.2023.2282231

Repository Public URL： https://hdl.handle.net/2324/7159364

Language：English   Publishing type：Research paper (scientific journal)  

The fatigue crack propagation properties of newly-developed SM490 grade steels were investigated in comparison with a conventional steel of the same grade.
The fatigue crack propagation rate of the developed steel in Region II of the da/dN-ΔK relationship was suppressed to about 1/2 that of the conventional steel, and its ΔKth value was more than twice as large as in the conventional steel.
However, fatigue crack resistance for long crack propagation does not necessarily improve the fatigue life in a condition of increasing ΔK from a small defect, which is usually detected in practical fatigue damage in actual structures in service.
The developed steels were subjected to surface crack propagation tests using specimens with artificial small defects to examine their potential under more practical conditions.
The fatigue life of the developed steel was about three times longer than that of the conventional steel. A detailed analysis of the surface crack propagation revealed crack propagation below ΔKth only in the developed steels, which suggested the so-called “short crack regime” in a fatigue crack.
The crack propagation from a surface defect that deviated from long crack behavior was convincingly explained by the corrected threshold using the R-curve model of a short crack proposed in the previous literature.
Based on the experimental fatigue life improvement and its analytical estimation of the propagation resistance in the short crack regime, the effect of the ΔKth value for a long crack in the initial propagation stage just after fatigue crack initiation was discussed.

DOI： https://doi.org/10.2355/isijinternational.ISIJINT-2023-168

Repository Public URL： https://hdl.handle.net/2324/7238744

Language：English   Publishing type：Research paper (international conference proceedings)  

The purpose of this paper is to confirm fatigue strength of welded joints can be improved by grain refinement using laser irradiation and localized carburization considering corrosion and abrasion.
The measured temperature histories due to laser irradiation were compared with theoretical solutions for moving and instantaneous line heat sources, and it was confirmed that the temperature history could be estimated well using moving heat source. Maximum temperature and time required from 800 ℃ to 500 ℃ (Δt8/5) of the grain refinement region are obtained by applying moving heat source.

Four-point bending fatigue tests were conducted on T-joint specimens as welded, laser irradiated, and locally carburized.
As a result, number of cycles to failure of the specimens which locally carburized and laser irradiated were equivalent and they are longer than that of the specimens as-welded.
The main reason is locally carburized and laser irradiated had more gentler toe shapes than as-welded.
However, the porosity was observed in the carburized specimen.
It can affect fatigue strength, further improvement of fatigue strength was expected by eliminating it.

Other Link： https://team2023.pknu.ac.kr/

Repository Public URL： https://hdl.handle.net/2324/7157262

Language：English   Publishing type：Research paper (international conference proceedings)  

Laser-arc hybrid welding (LAHW) is an advanced welding process that combines arc and laser welding as one molten pool.
Compared with conventional arc welding, LAHW can be performed higher welding speeds with narrower grooves, and weld deformation can be significantly reduced.
When LAHW is applied to construction of structural members, the welding is generally performed in a flat position because it is automatic welding system is applied from the viewpoint of safety in the work environment.
Flat position (PA), it is expected to be applied to many welds of large steel structures by applying LAHW to horizontal position.
However, the application of LAHW in the construction of large structures is expected by expanding the applicable welding position.
In this study, butt joints with a plate thickness of 20 mm were fabricated in the horizontal position (PC) as a target of welding position in LAHW.
By trial and error, referring to the welding conditions in the flat position, the welding conditions that produced a sound weld bead appearance were derived.
However, molten metal was sagging at some of lower weld bead edge of the front bead. A sliding jig was designed to prevent the front bead sagging.
As a result, the sagging was prevented and it was expected that the jig was effective in relaxing the shape of the weld toe for improving the fatigue strength of the joint.
In the construction stages of large structures, it is difficult to maintain a constant root gap over the entire length of the weld line, so it is desirable to extend the allowable range of the initial gap. Therefore, we attempted to process with an initial root gap of 1.5 mm.
However, we were unable to find welding conditions that would avoid undercutting and melting-in, and confirmed that the applicable limit of the initial root gap is 1.0 mm for the construction method studied in this study.

Other Link： https://team2023.pknu.ac.kr/

Repository Public URL： https://hdl.handle.net/2324/7157020

Language：English   Publishing type：Research paper (international conference proceedings)  

In numerical simulations of fatigue crack propagation, the true stress-true strain relationship under cyclic loading should be considered, but in simulations modelling crack opening behaviour, the stress-strain relationship of the material is regarded as rigid plastic or isotropically hardened elastic-plastic material from the point of view of model simplification.
In this study, the true stress-true strain relationship under cyclic loading, estimated from the true stress-true strain relationship under monotonic tensile loading, is implemented in fatigue crack propagation simulations of work-hardened materials proposed by some of authors.
Fatigue crack growth curves under the following three loadings, (1) constant cyclic loading under different stress ratios, (2) two-stage block loading cycles, (3) constant cyclic loading with a spike load, were estimated and compared with the measured results obtained in previous studies.
The results show that the accuracy of the fatigue crack growth estimation is better than the conventional stress-strain relationship assuming elastic-perfectly plastic materials.

Other Link： https://team2023.pknu.ac.kr/

Repository Public URL： https://hdl.handle.net/2324/7157018

Language：Japanese   Publishing type：Research paper (other academic)  

Study on fabrication of butt welded joints of thick plates by laser-arc hybrid welding in horizontal position (PC),
Toshiki Tsuruoka, Tomoya Uchimura, Koji Gotoh,
Proceedings of Japan Welding Society, Kyushu-chapter，No. 20 (2023), 5-8.

Repository Public URL： https://hdl.handle.net/2324/6796166

Language：Japanese   Publishing type：Research paper (other academic)  

Study on a method of one-pass construction of thick plates by laser/arc hybrid welding without the use of backing material,
Hiroo Kobayashi, Toshiki Tsuruoka, Tomoya Uchimura, Koji Gotoh,
Proceedings of Japan Welding Society, Kyushu-chapter，No. 20 (2023), 1-3.

Repository Public URL： https://hdl.handle.net/2324/6796165

Language：Japanese   Publishing type：Research paper (scientific journal)  

Cyclic true stress true strain relation in the large strain region of common steel for welded structures,
Kazuki MATSUDA, Tsukasa SHIMOKA, Koji MURAKAMI, Tomoya UCHIMURA, Koji GOTOH,
QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY, 2023 Volume 41 Issue 3 Pages 217-224
https://doi.org/10.2207/qjjws.41.217

DOI： https://doi.org/10.2207/qjjws.41.217

Repository Public URL： https://hdl.handle.net/2324/6794871

Language：Japanese   Publishing type：Research paper (other academic)  

Experimental Investigation on Stress-Strain Relationship of Steel under Cyclic Loading,
Tsukasa Shimooka, Koji Murakami, Kazuki Matsuda and Koji Gotoh,
Proceedings of Japan Welding Society, Kyushu-chapter，No. 19 (2022), 1-4.

Repository Public URL： http://hdl.handle.net/2324/4798534

Language：Japanese   Publishing type：Research paper (other academic)  

Study on the Application of Laser-arc Hybrid Welding with REM Additive Welding consumables in the Hull Construction Stage,
GOTOH Koji, NAKADA Tomoya, UCHIMURE Tomoya, ANDO Akiyoshi, MATSUSHITA Muneo, HANDA Tsunehisa and IGI Satoshi,
Preprints of the National Meeting of JWS, No. 111, September 2022, 146-147.

Repository Public URL： http://hdl.handle.net/2324/4822577

Language：Japanese   Publishing type：Research paper (other academic)  

A Study on Prediction of Fillet Weld Bead Shape Using Machine Learning with Welding Conditions and Welding Noise as Input Variables
Yong-Yi Feng, Norihiro Watanabe, Kento Yamazaki, Kazuki Matsuda, Koji Gotoh,
Proceedings of Japan Welding Society, Kyushu-chapter，No. 19 (2022), 41-44.

Repository Public URL： http://hdl.handle.net/2324/4822551

Language：Japanese   Publishing type：Research paper (other academic)  

Basic Study on Grain Refinement by Laser Irradiation for Fatigue Strength Improvement
Kazuyuki Teratsuji, Tomoya Uchimura, Kazuki Matsuda and Koji Gotoh,
Proceedings of Japan Welding Society, Kyushu-chapter，No. 19 (2022), 37-40.

Repository Public URL： http://hdl.handle.net/2324/4822550

Language：English   Publishing type：Research paper (international conference proceedings)  

The development of an automatic weld visual inspection system applicable to weld bead visual inspection in shipyards is expected to reduce costs through man-hour reduction, improve weld quality, and shorten the repair process.
Although many studies have been conducted on the automation of weld bead visual inspection, most of them were based on image analysis.
However, in order to apply image analysis, it is necessary to remove residual slag from the bead surface after welding before taking images, which is not desirable considering the production process in shipyards.
The author's research group has been studying a method to predict weld bead appearance by deep learning using welder log data (current, voltage, and welding wire feed rate) and fixed welding conditions (torch angle, etc.) as inputs.
In this study, several improvements were made to the prediction of the leg length and undercut depth of the T-shaped joint. These improvements significantly improved the adjusted coefficient of determination, a measure of prediction accuracy, to 0.96 for leg length prediction and 0.93 for undercut depth prediction, resulting in improved prediction accuracy for leg length and undercut depth.

Repository Public URL： http://hdl.handle.net/2324/4822552

Language：English   Publishing type：Research paper (international conference proceedings)  

This study is concerned with the development of a system for automatically carrying out visual inspections of the external appearance of welders in the welder's skills certification examination, without requiring extensive experience in visual inspections, and presents the results of the development of a prototype of such a system.
The developed system handles the weld bead shape measured with a 3D scanner as point data in 3D space, and matches it with the evaluation criteria for the welder qualification test, such as bead width, reinforcement of weld height and undercut depth, to enable a pass/fail decision to be made immediately after the test is taken.
In addition, the joint geometry can be stored as high-precision point cloud digital data, allowing another visual inspection to be carried out even after the specimen has been processed for bending tests after visual inspection.

Repository Public URL： http://hdl.handle.net/2324/4822553

Language：Japanese   Publishing type：Research paper (other academic)  

Basic Research on Local Carburizing Treatment by Laser Irradiation for Fatigue Strength Improvement of Welded Joints,
Takehiro Tamon, Koji Gotoh, Yasuhiro Morizono
Conference Proceedings of JASNAOE, Vol.34, 2022, pp.467-472, 2022S-GS10-5

Repository Public URL： http://hdl.handle.net/2324/4793671

Language：Japanese   Publishing type：Research paper (other academic)  

A Study on Frame Length and Frame Shift of Training Data for Automatic Inspection of Weld Bead Appearance Using Deep Learning,
Norihiro Watanabe, Kento Yamasaki, Koji Gotoh,
Conference Proceedings of JASNAOE, Vol.34, 2022, pp.259-261, 2022S-GS1-5

Repository Public URL： http://hdl.handle.net/2324/4794181

Language：Japanese   Publishing type：Research paper (other academic)  

Experimental and Analytical Study on Wear Coefficient of Mooring Chain by Using 3-D Measurement,
Takaaki Murakami, Takaaki Takeuchi, Tomoaki Utsunomiya, Koji Gotoh,
Conference Proceedings of JASNAOE, Vol.34, 2022, pp.251-257, 2022S-GS1-4

Repository Public URL： http://hdl.handle.net/2324/4794429

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Study on Practical Fabrication Method in Tee Type Full Penetrated Welded Jointunder Long Distance Welding Fabricated by the Laser-Arc Hybrid Welding,
Takamori Uemura, Tomoya Uchimura and Koji Gotoh
Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol. 34, 2021, pp.197-207.

Repository Public URL： http://hdl.handle.net/2324/4763156

Language：Japanese   Publishing type：Research paper (scientific journal)  

Experimental Study on Wear Coefficient of Mooring Chain for Floating Offshore Structures
Takaaki Murakami，Takaaki Takeuchi，Tomoaki Utsunomiya and Koji Gotoh
Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol. 34, 2021, pp.63-71.

Repository Public URL： http://hdl.handle.net/2324/4763197

Language：English   Publishing type：Research paper (international conference proceedings)  

Since the serious factor of damages in welded structures is generally fatigue and fracture originating from fatigue cracks.
Fatigue cracks in welded structures usually initiate at the weld toe. High frequency mechanical impact treatment (HFMI) and peening are well known techniques to improve the fatigue life of structures.
Most of these treatments for fatigue life improvement have to be carried out after welding, which is an extra step in terms of productivity.
It is therefore desirable to be able to carry out fatigue strengthening treatment of welded joints continuously after welding on the same working line. As one of the methods, the authors have shown that local laser irradiation near the weld toe can improve the fatigue life by relaxing the stress concentration and by refining the grains in the irradiated area.
However, in the case of long-term operation such as in ships and offshore structures, there is a concern that the improved weld toe geometry and grain refinement area may be lost over time due to corrosion.
In order to cope with this situation, the authors found the possibility to apply the local carburizing of the weld toe area by laser irradiation.
In this study, the conditions of the laser irradiation were investigated for the local carburizing.
A certain amount of carbon was applied to the surface of mild steel plates, and the relationship between the laser irradiation conditions and the degree of hardening (width of hardened area and hardness value of the hardened layer) was investigated experimentally.
From the results it was concluded that the hardness of the fusion zone could be evaluated in relation to the size of the fusion zone and the amount of the mixed carbon component.
Next, based on the above hypothesis, local laser carburizing was carried out on the weld toes produced by arc welding, and the results showed the same tendency as in the basic investigation.
However, porosities of various sizes generated in the fusion zone, and the degree of porosities varied with the steel grade.
The cause of the porosities is thought to be a gasification reaction between the oxygen and carbon components in the steel or mixed in from the atmosphere.
In general, the presence of oxygen is one of the most serious problems causing abnormal areas in actual carburizing, and in laser carburizing characterized by rapid heating and cooling, this problem is thought to be responsible for the occurrence of porosities.
The result of this study suggest that the deoxidizing agent, silicon (Si) component, is significantly effective in controlling the porosities in order to form a sound carburizing layer at the weld toe.

Language：English   Publishing type：Research paper (international conference proceedings)  

With global warming on the rise, various initiatives are being taken to promote the use of renewable energy sources to reduce greenhouse gas emissions.
In particular, there are high expectations for the expansion of offshore wind power due to its high generating capacity.
One of the challenges for the widespread use of offshore wind turbines is to reduce maintenance costs, especially for moorings.
The floating motion of moored offshore wind turbines causes wear on the mooring chains. As the wear progresses, there is a possibility of rupture.
In order to ensure the safety of floating offshore wind turbines, it is essential to establish a method for assessing the amount of wear on the mooring chain.
This will enable an appropriate maintenance plan to be drawn up for the mooring system.
This allows maintenance costs to be taken into account at the planning stage of the installation.
It also identifies the challenges to achieving a maintenance-free system.
Regarding the evaluation of wear of mooring chains for offshore wind turbines, Takeuchi et al. proposed a method for estimating the amount of wear based on the results of a floating response analysis that evaluates the tension acting on the chain and the sliding and rotation between the links.
In this estimation method, a simple estimation equation as a function of inter-link tension and angle is applied.
This simplified estimating equation is based on experiments to reproduce the wear behavior of mooring chains conducted in air environment or by dripping artificial seawater or freshwater on the contact area.
However, in order to evaluate the wear development more quantitatively, it is necessary to conduct experiments with mooring chains completely submerged in water and reflect the results of the experiments.
The experimental system was constructed to reproduce the wear behavior of a mooring chain with dimensions similar to those of the in-service machine, when it is completely submerged in water.
The wear behavior was investigated under several tension conditions, and it was confirmed that the wear behavior in a fully submerged environment was different from that in air or in liquid drops.

Language：Japanese   Publishing type：Research paper (other academic)  

A Study on Automatic Hyperparameter Search Method and Input Data Processing Method for Automatic Inspection of Weld Bead Appearance Using Deep Learning,
Norihiro Watanabe, Kento Yamasaki and Koji Gotoh
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.33, November 2021, pp.337-339, 2021A-GS7-4.

Language：Japanese   Publishing type：Research paper (other academic)  

Approach to Optimistic Process of Tack Welding by Laser in Butt Joint,
Takamori Uemura and Koji Gotoh
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.33, November 2021, pp.341-345, 2021A-GS7-5.

Language：Japanese   Publishing type：Research paper (other academic)  

Study on extending the thickness range of transverse horizontal welding in laser-arc hybrid welding,
Tomoya Nakada, Tomoya Uchimura, Takamori Uemura and Koji Gotoh,
Proceedings of Japan Welding Society, Kyushu-chapter，No. 18 (2022), 29-32

Repository Public URL： https://hdl.handle.net/2324/6757884

Language：Japanese   Publishing type：Research paper (other academic)  

Study on the measurement of the alternating plastic zone size at the tip of a fatigue crack using a digital image correlation method,
Naoki Ojima, Koji Murakami and Koji Gotoh,
Proceedings of Japan Welding Society, Kyushu-chapter，No. 18 (2022), 21-24.

Repository Public URL： https://hdl.handle.net/2324/6757890

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Study of Automatic Measurement Method of RPG (Re-tensile Plastic zone’s Generated) load,
Koj MURAKAMI, Mizuki MORISHITA, Koji GOTOH,
Quarterly Journal of the Japan Welding Society, 2021 Volume 39 Issue 2 Pages 125-131.
DOI https://doi.org/10.2207/qjjws.39.125

DOI： https://doi.org/10.2207/qjjws.39.125

Repository Public URL： http://hdl.handle.net/2324/4794831

Language：English   Publishing type：Research paper (international conference proceedings)  

The fabrication of ship hulls involves welding operations, one typical operation is fillet welding of stiffeners to plates (panels) a so-called T-joint.
The residual stresses from the welding process will influence the fatigue life of the structure, and residual deformations will increase the risk for buckling of the panel and give poor fabrication tolerances which may complicate the assembly of a built-up structure.

Though this weld geometry has been frequently studied in the literature both experimentally and numerically, the focus has been on the residual stress field and if residual deformations are studied, the angular distortion and the typical V-shape seen in the welded plate (panel) are reported.
This benchmark focusses on the residual shape after two-pass fillet welding of a stiffener to a plate (T-joint and the influence of the constraints used during welding. The information of the full welding residual deformations may be useful for the fabrication of larger complex welded structures.

The benchmark study clearly shows that careful consideration is needed when defining a reference plane for comparison of resulting deformations from FE-simulations and from experiments as well as good documentation of the actual boundary conditions and steps carried after the completion of the welding and before measuring residual deformations.
The FE-simulations have shown that it is difficult to obtain the full antisymmetric, twisted shape of the plate as measured in the experiments, although a trend similar to the experiments can be seen as the plate tends to move upwards at the end of each weld pass, i.e a slight influence of the weld pass direction.

DOI： https://doi.org/10.1115/OMAE2022-87473

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Study on Improvement of Fatigue Performance by Shot Blasted Surface Treatment,
Toshihiro Fujii, Koichi Okada, Jun-ichi Deguchi and Koji Gotoh,
Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol.33, June 2021, pp.97-106.

DOI： https://doi.org/10.2534/jjasnaoe.33.97

Repository Public URL： http://hdl.handle.net/2324/4794834

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack Propagation Considering the Alternating Plastic Behavior that Occurs Near the Crack Tip Using Elastic-Plastic Finite Element Analysis,
Kenya Yamaguchi and Koji Gotoh
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.32, May 2021, pp.417-422, 2021S-GS9-3.

Language：Japanese   Publishing type：Research paper (other academic)  

Development of Mooring Chain Wear Behavior Reproduction Test Machine in Underwater Environment,
Koji Gotoh, Koji Murakami, Tomoaki Utsunomiya and Iku Sato
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.32, May 2021, pp.389-392, 2021S-GS8-1.

Language：Japanese   Publishing type：Research paper (other academic)  

A Study on Practical Fabrication Method in Tee Type Full Penetrated Welded Joint under Long Distance Welding Fabricated by the Laser-Arc Hybrid Welding,
Takamori Uemura, Koji Gotoh, Issei Uchino, Tomoya Uchimura and Koji Murakami
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.32, May 2021, pp.433-438, 2021S-GS10-3.

Language：Japanese   Publishing type：Research paper (other academic)  

Studies on Expansion of Laser-Arc Hybrid Welding to Horizontal and Vertical-Up Welding,
Takamori Uemura, Koji Gotoh, Issei Uchino, Tokio Fukuda, Tomoya Uchimura and Koji Murakami
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.32, May 2021, pp.427-431, 2021S-GS10-2.

Language：Japanese   Publishing type：Research paper (other academic)  

Proposal of Simplified Wear Estimation Method for Mooring Chain of Floating Structures by Considering Roll-Up Motion,
Takaaki Takeuchi, Tomoaki Utsunomiya, Koji Gotoh and Iku Sato,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.32, May 2021, pp.393-401, 2021S-GS8-2.

Language：English   Publishing type：Research paper (scientific journal)  

Long-term operation of mooring systems is one of the challenging issues of floating structures such as floating offshore wind turbines (FOWTs).
For integrity assessment, fatigue and its affecting factors have generated considerable recent research interest as the occurrence of a large number of mooring chain failures at a high rate has been reported.
By contrast, only few studies on the effect of nonuniform volume loss of mooring chain links due to wear can be found because of difficulties to estimate wear amounts quantitatively.
Considering this issue, in this paper, validation of the quantitative interlink wear estimation method is investigated by applying to a spar-type floating structure.
Firstly, the method is presented which consists of the material test, derivation of an interlink wear estimation formula with FE analysis, and calculation of mooring chain response with coupled dynamic analysis using a mass-spring model.
To improve insufficient accuracy due to the mass-spring model around a clump weight and the touchdown point, the method is further modified by using a 3-D rigid-body link model.
The estimation results and comparison show that the modified method distinguishing between rolling and sliding can calculate the interlink wear amount closer to the chain diameter measurements and more reasonable than the method using the conventional mass-spring mode

DOI： https://doi.org/10.1016/j.marstruc.2020.102927

Language：Japanese   Publishing type：Research paper (scientific journal)  

Studies on applying hot-rolled coil to hull superstructure,
Hisao Narimatsu, Takamori Uemura, Masakazu Kuwada and Koji Gotoh,
Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol.32, December 2020, pp.247-257.

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Study on Adopting Λ-Shape Groove for Laser-Arc Hybrid Welding to Construct Thick Plate Butt Welded Joints,
UCHINO Issei，UEMURA Takamori and GOTOH Koji,
Quarterly Journal of the Japan Welding Society, Vol. 38, (2020), Issue 4, pp.403-417.

DOI： https://doi.org/10.2207/qjjws.38.403

Language：Japanese   Publishing type：Research paper (other academic)  

Fundamental Study on Improving Fatigue Life of Welded Joints Locally Carburized by Laser Irradiation,
Takehiro TAMON, Takamori, UEMURA and Koji GOTOH,
Proceedings of Japan Welding Society, Kyushu-chapter, No.17, 2020, pp.17-20.

Language：Japanese   Publishing type：Research paper (other academic)  

Repository Public URL： http://hdl.handle.net/2324/4794747

Language：Japanese   Publishing type：Research paper (scientific journal)  

Quantitative Wear Estimation for Mooring Chain of Floating Structures and Its Validations,
Takaaki Takeuchi, Tomoaki Utsunomiya, Koji Gotoh and Toshio Niwa,
Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol.30, December 2019, pp.131-141.

Language：Japanese   Publishing type：Research paper (other academic)  

Repository Public URL： http://hdl.handle.net/2324/4794744

Language：Japanese   Publishing type：Research paper (other academic)  

Repository Public URL： http://hdl.handle.net/2324/4794745

Language：Japanese   Publishing type：Research paper (other academic)  

Verification of RFID Availability for Hull and Fitting Parts Logistics Management at Shipyard,
Shun-ichi Akagi, Satoshi Ito, Shingo Onodera, Ryousuke Ota, Yasuhiko Takaishi, Kazuhiro Hirao and Koji Gotoh,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.29, November 2019, pp.339-342, 2019A-GS13-4.

Language：Japanese   Publishing type：Research paper (other academic)  

A Study on Improvement of Fatigue Performance by Shot Blasted Surface Treatment (Part 2)Verification for butt welded joints,
Toshihiro Fujii, Koichi Okada, Jun-ichi Deguchi and Koji Gotoh,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.29, November 2019, pp.359-362, 2019A-GS14-4.

Language：English   Publishing type：Research paper (international conference proceedings)  

Application of the hot-rolled steel sheet for the members of superstructure, where the strength requirement of these parts in ships is not severe, is expected as a solution to reduce the hull construction cost.
Because the hot-rolled steel sheet is applied after recoiling by cold working to return it to a flat plate, the material properties is deteriorated due to excessive plastic working and the residual stress induced by the plastic work might affect for the thermal cutting and welding.
There is a possibility that the hot-rolled steel sheet has poor properties comparing with the flat rolled steels applied for hull parts where the structural integrities are required by the classification societies’ rules.
The difference of properties between the hot-rolled steel sheet and the flat rolled steel are investigated in this research.
Investigated items are mechanical properties, microstructures, initial residual stress distributions, hardness distributions, distortion after thermal cutting and laser-arc hybrid welding.

DOI： https://doi.org/10.1007/978-981-15-4680-8

Repository Public URL： http://hdl.handle.net/2324/4752586

Language：Japanese   Publishing type：Research paper (scientific journal)  

Proposal of Wear Estimation Method for Mooring Chain of Floating Structures,
Takaaki Takeuchi, Kimihiro Toh, Tomoaki Utsunomiya and Koji Gotoh
Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol.29, June 2019, pp.77-87.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Proposal of Wear Estimation Method for Mooring Chain of Floating Structures
Takaaki Takeuchi, Kimihiro Toh, Tomoaki Utsunomiya, Koji Gotoh,
Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol.29, June 2019, pp.77-87.

DOI： https://doi.org/10.2534/jjasnaoe.29.77

Language：Japanese   Publishing type：Research paper (other academic)  

Fundamental Investigation of Numerical Simulation of Fatigue Crack Propagation Considering the Cyclic Plasticity in the Vicinity of a Crack Tip Based on the Strip Yield Model,
Kenya YAMAGUCHI, Koji GOTOH,
Proceedings of Japan Welding Society, Kyushu-chapter, No.16, 2019, pp.25-28.

Language：Japanese   Publishing type：Research paper (other academic)  

Preliminary investigation for the extention of applicable welding position in laser arc hybrid welding
Tokio FUKUDA, Musashi HARA, Takamori UEMURA, Koji MURAKAMI and Koji GOTOH,
Proceedings of Japan Welding Society, Kyushu-chapter, No.16, 2019, pp.21-24.

Language：Japanese   Publishing type：Research paper (other academic)  

Fundamental Study of Automatic Inspection of Weld Bead Appearance based on welding parameters by Machine Learning
Musashi HARA, Norihiro, WATANABE, Naoki MORIHIRA and Koji GOTOH,
Proceedings of Japan Welding Society, Kyushu-chapter, No.16, 2019, pp.17-20.

Language：Japanese   Publishing type：Research paper (other academic)  

Quantitative Wear Estimation for Mooring Chain of Floating Structures and Its Validation
Takaaki Takeuchi, Tomoaki Utsunomiya, Koji Gotoh, Iku Sato,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.28, June 2019, pp.343-349, 2019S-GS11-3.

Language：Japanese   Publishing type：Research paper (other academic)  

Fundamental Investigation of Numerical Simulation of Fatigue Crack Propagation Considering the Cyclic Plasticity in the Vicinity of a Crack Tip Based on the Strip Yield Model,
Kenya Yamaguchi, Koji Gotoh,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.28, June 2019, pp.463-466, 2019S-GS18-4.

Language：Japanese   Publishing type：Research paper (other academic)  

Joint Industrial Project on the Introduction of Laser-Arc Hybrid Welding Technology to Hull Construction Process　- (Part 4) Construction Trial of Butt Welded Joint with Long Welding Length -
Koji Gotoh, Takamori Uemura, Issei Uchino, Koji Murakami, Atsuo Moriyama
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.28, June 2019, pp.277-282, 2019S-GS8-4.

Language：Japanese   Publishing type：Research paper (other academic)  

Joint Industrial Project on the Introduction of Laser-Arc Hybrid Welding Technology to Hull Construction Process　- (Part 3) Construction Trial of Full-Penetration Tee Joint with Long Welding Length Fabricated by One-Side Single Pass Welding -
Koji Gotoh, Takamori Uemura, Koji Murakami, Toshimitsu Maeda, Takumi Torigoe, Atsuo Moriyama
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.28, June 2019, pp.271-275, 2019S-GS8-3.

Language：Japanese   Publishing type：Research paper (other academic)  

Joint Industrial Project on the Introduction of Laser-Arc Hybrid Welding Technology to Hull Construction Process - (Part 2) Influence of Factors on Weldability -
Koji Gotoh, Ryuhei Takeshita, Takamori Uemura, Atsuo Moriyama,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.28, June 2019, pp.265-269, 2019S-GS8-2.

Language：Japanese   Publishing type：Research paper (other academic)  

Joint Industrial Project on the Introduction of Laser-Arc Hybrid Welding Technology to Hull Construction Process - (Part 1) Deriving Welding Conditions and Evaluating Joint Quality of Full-Penetration Tee Joint Fabricated by One-Side Single Pass Welding -
Koji Gotoh, Shuichi Tsumura, Toshiaki Iwata, Atsuo Moriyama
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.28, June 2019, pp.261-264, 2019S-GS8-1.

Language：Japanese   Publishing type：Research paper (other academic)  

Fundamental Study of Automatic Inspection of Weld Bead Appearance by Machine Learning
Naoki Morihira Norihiro Watanabe, Koji Gotoh,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.28, June 2019, pp.259-260, 2019S-GS7-2.

Language：Japanese   Publishing type：Research paper (other academic)  

Overview of Joint Industrial Project on the Introduction of Laser-Arc Hybrid welding to the Hull Construction Stage in Japanese Shipyard,
Koji GOTOH, Takamori UEMURA, Issei UCHINO, Hisao NARIMATSU, Toshimitsu MAEDA, Takumi TORIGOE, Atsuo MORIYAMA,
Proceedings of Japan Laser Processing Society, No.91, June, 2019, pp.67-74.

Repository Public URL： http://hdl.handle.net/2324/4794502

Language：English   Publishing type：Research paper (international conference proceedings)  

Recently, the strength of the hull structure including fatigue strength has seen significant improvement because of application of IACS CSR (Common Structure rule), developed by IACS.
Various methods which can increase the fatigue strength at welded joints are suggested, since the damage morphology on the recently welded structures was observed to be primarily fatigue failure.
In Shipbuilding industry, smoothening of the welding bead toe by grinding is the method that is customarily adopted in order to increase fatigue strength.
And recently, peening treatment at the welding bead has also been adopted.
The peening treatment can reduce stress concentration by smoothening of the welding bead toe, and a compressive residual stress field generated by the impact of peening.
In case of generating compressive residual stress by impact, the same effect could be expected by shot blasting, which is the steel surface treatment before painting.
In this study, the condition of the residual stress generated at welding toe by shot blasting was investigated, and then from results of the fatigue test, the increase in fatigue strength due to residual stress is verified.

Repository Public URL： http://hdl.handle.net/2324/4753062

Language：English   Publishing type：Research paper (international conference proceedings)  

Austenitic stainless steels such as SUS 316 LN and austenitic stainless clad steel are used in cargo holds of chemical tankers owing to their corrosion resistance.
Recently, the use of duplex stainless steels has been increasing, owing to their better strength and corrosion resistance and lower content of expensive Ni, compared with those features of austenitic stainless steels.
However, few duplex stainless clad steels have been approved by classification bodies. Furthermore, the application of duplex stainless steel is not yet mainstream as hull structural materials because a stable supply market has yet to be established.
Therefore, when applying cladding steel to construction of chemical tankers, austenitic stainless clad steel is often used at present.
The duplex stainless steel and the austenitic stainless clad steel are mixed at construction factories; hence, there is a risk of misuse of welding consumables.
If misuse is suspected, it is not possible to judge the erroneous use from visual inspection after construction; therefore it is necessary to uniformly remove the weld and re-weld.
However, if universal welding consumables were identified, this might avoid the problems of misuse and simplify the procurement of welding materials.
In this paper, we report on our studies to verify welding consumables for use in the hull structures, involving a mixture of duplex stainless steel and the austenitic stainless clad steel.
The static strength of the welded joints is a particular focus of this study, from which we confirmed the validity and limitations of welding consumables.

Repository Public URL： http://hdl.handle.net/2324/4753063

Language：English   Publishing type：Research paper (international conference proceedings)  

The application of advanced welding technologies is important for improving the efficiency of hull construction processes and reducing production costs. Laser-arc hybrid welding technology, which combines the advantages of laser and normal arc welding, is of high quality and is expected to improve productivity.
The Japan Ship Technology Research Association has organized the joint industry project in collaboration with a university, a classification society and some shipyards to apply this technology in the construction of general merchant ships, in which the plate thickness of the main structural member is thicker than passenger ships and high speed craft.
Main research achievements are as follows.
1) Establishment of welding procedure to fabricate the full-penetration tee joint by one-side single-pass welding.
2) Confirmation of the influence of weld groove processing method (laser, plasma or gas cutting) and residual primer and oxide film on the quality of butt welded joint fabricated by the I shaped groove preparation and one pass welding and confirming the effectiveness of spatter reduction technique by applying the J-STAR® Welding as an arc welding.

Repository Public URL： http://hdl.handle.net/2324/4755271

Language：Japanese   Publishing type：Research paper (scientific journal)  

Experimental Study on Specific Wear of Mooring Chain for Floating Structure,
Koji Gotoh, Tomoaki, Utsunomiya, Masataka Nakagawa and Kazuki Yamane,
Journal of the Japan Society of Naval Archtects and Ocean Engineers,
Vol.28, 2018, pp.145-154.

DOI： https://doi.org/10.2534/jjasnaoe.28.145

Repository Public URL： http://hdl.handle.net/2324/4794500

Language：Japanese   Publishing type：Research paper (other academic)  

Study on Unification of Welding Consumables in Construction of Chemical Cargo Tanker Made of
Duplex Stainless Steel - (Part 1) Evaluation of Static Strength of Welded Joint,
Takayuki Yotsuzuka, Eiji Niino, Yusuke Endo and Koji Gotoh,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.27, November 2018, pp.317-322, 2018A-GS9-2.

Language：Japanese   Publishing type：Research paper (other academic)  

A Study on using Hot-Coil Steel for Superstructure,
Hisao Narimatsu, Masakazu Kuwada, Koji Gotoh and Yuki Sugino,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.27, November 2018, pp.455-459, 2018A-GS17-2.

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Surface Crack Propagation under In-plane Biaxial Cyclic Loadings with Phase Differences,
Mizuki Morishita, Koji Gotoh, Yosuke Anai and Toshio Niwa,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.27, November 2018, pp.439-444, 2018A-GS16-3.

Language：Japanese   Publishing type：Research paper (other academic)  

A Study on Improvement of Fatigue Performance by Shot Blasted Surface Treatment
Toshihiro Fujii, Koji Gotoh, Jun-ichi Deguchi and Koji Murakami,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vo.27, November 2018, pp.429-433, 2018A-GS16-1.

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical investigation of gap allowance of butt welded joint applied to hull component by laser-arc hybrid welding,
Takamori UEMURA, Yuki SUGINO, Issei UCHINO and Koji GOTOH,
Proceedings of Japan Welding Society, Kyushu-chapter, No.15, 2018, pp.53-56.

Language：Japanese   Publishing type：Research paper (other academic)  

Angular distortion of butt welded joint manufactured using hot rolled steel sheet and laser-arc hybrid welding,
Yuki SUGINO, Takamori UEMURA,Hisao NARIMATSU and Koji GOTOH,
Proceedings of Japan Welding Society, Kyushu-chapter, No.15, 2018, pp.53-56.

Language：Japanese   Publishing type：Research paper (other academic)  

Study on Wear Estimation Method and Dynamic Behavior for Mooring Chain of Floating Structures，
Takaaki Takeuchi, Tomoaki Utsunomiya and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.26, 2018S-GS6-3, pp.269-274.

Language：Japanese   Publishing type：Research paper (other academic)  

Investigation on Specific Wear Amount of Mooring Chain by Pin-on-disk Wear Test，
Kazuki Yamane, Masataka Nakagawa, Tomoaki Utsunomiya and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.26, 2018S-GS6-2, pp.263-267.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Practical Determination Method of the Threshold Stress Intensity Factor Range ΔKth,
MURAKAMI Koji and GOTOH Koji,
Quarterly Journal of Welding Society, Vol.35, No.4, (2017), pp.149-153.
https://doi.org/10.2207/qjjws.35.149

DOI： https://doi.org/10.2207/qjjws.35.149

Repository Public URL： http://hdl.handle.net/2324/4794496

Language：Japanese   Publishing type：Research paper (other academic)  

Extension of the stress intensity factor weight function for a surface crack and estimation of crack opening displacement based on Paris' reciprocity theorem,
Koji Murakami and Koji Gotoh,
Proceedings of Japan Welding Society Weld Structure Symposium 2017, pp.265-268.

Repository Public URL： http://hdl.handle.net/2324/4794493

Language：Japanese   Publishing type：Research paper (other academic)  

A Study of measurement accuracy of RPG load of the fatigue crack propagation test,
Koji Murakami and Koji Gotoh,
Proceedings of Japan Welding Society Weld Structure Symposium 2017, pp.253-256.

Repository Public URL： http://hdl.handle.net/2324/4794495

Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue Crack Growth Behaviour of an Out-of-plane Gusset Welded Joints under In-plane Biaxial Tensile Loadings with Different Phases，
Koji Gotoh, Keishi Shimizu, Yosuke Anai and Toshio Niwa,
Journal of The Japan Society of Naval Architects and Ocean Engineers,
Vol.26, 2017, pp.157-164.

Repository Public URL： http://hdl.handle.net/2324/4794491

Language：Japanese   Publishing type：Research paper (scientific journal)  

Numerical Simulation of Fatigue Crack Propagation Considering Closure of Initial Defect Surfaces under Compressive Loading，
Yoshifumi Takaki and Koji Gotoh,
Journal of The Japan Society of Naval Architects and Ocean Engineers,
Vol.26, 2017, pp.131-136.

Repository Public URL： http://hdl.handle.net/2324/4794492

Language：Japanese   Publishing type：Research paper (other academic)  

Measurement of Alternating Plastic Deformation Region Near a Crack Tip under Cyclic Loading by the Digital Image Correlation Method，
Masanao Yamasaki, Koji Murakami and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.25, 2017A-GS2-14, pp.341-346.

Language：Japanese   Publishing type：Research paper (other academic)  

Shape Evolution of Fatigue Surface Crack under In-plain Biaxial Cyclic Loading，
Yosuke Anai, Toshio Niwa and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.28, 2017A-GS2-13, pp.337-340.

Language：English   Publishing type：Research paper (international conference proceedings)  

To promote the wind power generation plant on offshore area over the world, the floating wind turbine facility installed in the deep sea area plays an important role.
However, one of challenging issues related to the practical application of the commercial level of the floating facility installed in the deep sea area is the quantitative evaluation
of the wear behavior of the mooring chain, which is essential to reduce the maintenance and management costs of the floating structures.
Therefore, it is necessary to establish a quantitative wear evaluation method for mooring chains.
In this study, the experimental facility to reproduce the wearing phenomena occurring between links in actual scale due to the floating body motion caused by waves was constructed and the reproducibility of inter-links wear behavior was confirmed.
Subsequently, wear tests under some inter-links tensile forces was performed and the different abrasion behavior was observed because of the different inter-links tensile forces. Besides, possiblility of the numerical simulation to reproduce the experiments by applying the nonlinear finite element analysis with measured wear characteristics of applied material was confirmed.

Language：English   Publishing type：Research paper (international conference proceedings)  

It is necessary to identify relationship between the fatigue crack propagation rate and the stress intensity factor range, if the fracture mechanics approach is applied to evaluate the fatigue crack growth evolution.
In addition, identification of the stress intensity factor range of fatigue crack growth threshold DKth is important to evaluate the structural integrity from the view of fatigue performance.
ASTM standard E647 “Standard Test Method for Measurement of Fatigue Crack Growth Rates” is widely known as a de fact standard to determine the value of DKth.
However, a considerably long time is required to perform the determination of DKth.
Therefore, it is expected to shorten the experimental period for determination of DKth.
Efficient and time saving method for determining DKth comparing with ASTM-E647 is proposed in this study.
Many fatigue crack propagation test data were adopted to verify our proposed method.
It is expected to be able to complete the experiment for determining DKth at a stage where the fatigue crack propagation rate is one order larger than the test according to ASTM-E647.

Language：English   Publishing type：Research paper (international conference proceedings)  

The weight function of stress intensity factor is useful to determining stress intensity factor under arbitrary stress field.
In addition, the crack opening profile under arbitrary stress field can be determined by the reciprocity theorem concerning crack opening by Paris with the weight function of stress intensity factor.
Although many weight functions for a through thickness crack were proposed, the weight function for a surface crack is insufficient because of the limitation of applicable crack shape.
By considering that many cracks found in in-service welded structures are surface cracks, it is expected to develop the weight function for a surface crack with a wide range on crack shape.
One of authors had proposed practical formulae of the weight function for a surface crack based on the expression of the weight function by Wang and Glinka.
However, previous expression of the weigh function could not be applied in case of the deep crack of which the aspect ratio (crack depth / half crack length) is greater than 1.0.
Expansion of the weight function for a deep surface crack and minor modifications for previous weight function are conducted in this study.

Language：English   Publishing type：Research paper (international conference proceedings)  

Wear estimation method for mooring chain of floating facilities has not been established, and it currently relies on empirical methods.
In this research, an attempt was made to propose an estimation method for wear amount by combining 1) wear analysis between links of the mooring chain with finite element analysis and 2) response analysis of floating body-mooring system.
In addition, comparison was made for the estimated wear amount by this method with the measured wear amount in the actual sea area, in order to reveal whether this method is useful or not.
As a result, it was found that this method considerably overestimates the wear amount compared with the actual measurements.
One of the main reasons were supposed that elastic deformation of the mooring chain and external forces caused by tidal, current and wind were not taken into consideration and variations in the wear coefficient were large.

Language：English   Publishing type：Research paper (international conference proceedings)  

The shipbuilding industry in Japan is urgently required to develop and introduce advanced welding method to improve the efficiency of hull construction processes and the hull structural integrity and to reduce the production cost.
Laser-arc hybrid welding, which has the advantages of laser welding and arc welding, is expected to improve productivity.
However, some difficulties are concerned when laser-arc hybrid welding is applied for the construction stages of general merchant ships due to insufficient knowledge.
In this study, two research topics, which were the residual stress distribution and the angular distortion in the full-penetration tee joint fabricated and the influence of
groove cutting method on the quality of butt welded joint, were investigated.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue property in gigacycle regime is focused as an important subject in recent years.
In such a long-life region, a tremendous long period is required to perform the fatigue tests.
In order to overcome this difficulty, special types of fatigue testing machines in rotating bending whose loading type is cantilever bending has been developed.
It is known that this type of fatigue machine can be performed much quickly comparing with the tension and compression fatigue testing machines.
And these experimental results are consistent with much data obtained by using traditional testing machines like tension and compression fatigue testing machines and the rotating bending fatigue test machines whose loading type is uniform bending named as Ono type, though it is unclear that much data of an ultrasonic fatigue testing
machine are consistent with them.
Although it prefers to perform the fatigue tests as fast as possible, but the maximum frequency of a rotating bending fatigue test are limited because of the possibility of temperature rise in specimen caused by the cyclic plastic work and the heat transfer from fatigue testing machine.
Such local temperature rise might affect the fatigue property.
However, the appropriate loading frequency limit is unclear because of the difficulty of the temperature measurement in the fracture portion of a specimen precisely during the rotating bending fatigue test.
An in-situ temperature measuring technique is proposed to measure the temperature at the fracture portion of the specimen in real time during the fatigue testing, and the validity to determine the loading frequency of a rotating bending fatigue testing machine is discussed in this study.

DOI： 10.1299/transjsme.16-00535

Repository Public URL： http://hdl.handle.net/2324/4794488

Language：English   Publishing type：Research paper (international conference proceedings)  

Fatigue property in gigacycle regime is focused as an important subject in recent years.
In such a long-life region, a tremendous long period is required to perform the tests.
To overcome this difficulty, a part of authors has been developing the new rotating bending fatigue testing machine, which enables to reduce the test period and cost drastically.
It was confirmed that the fatigue test dates are consistent with many experimental results obtained by hydraulic tension and compression fatigue testing machines and the rotating bending fatigue test
machines of both-handed type known as Ono type.
Although it prefers to reduce the fatigue test period as short as possible, the maximum frequency of a rotating bending fatigue test is limited by the standards because of the possibility of local temperature rise in specimen caused by the cyclic plastic work and the heat transfer from fatigue testing machine.
Such local temperature rise might affect the fatigue property.
However, the appropriate loading frequency limit is unclear because of the difficulty of the temperature measurement in the fracture portion of a specimen precisely during the rotating bending fatigue test.
An in-situ temperature measuring technique is proposed to measure the temperature at the fracture portion of the specimen in real time during the fatigue testing, and the validity to determine the loading frequency of a rotating bending fatigue testing machine is discussed in this study.

Repository Public URL： http://hdl.handle.net/2324/4794497

Language：Japanese   Publishing type：Research paper (other academic)  

レーザ・アークハイブリッド溶接を一般商船の船体部に適用することをターゲットとした上で実用化に向けた課題の抽出，そして10kWを超えるレーザ出力を前提に各溶接パラメータの組合せが与える影響に関する基礎研究を行った．

Language：Japanese   Publishing type：Research paper (other academic)  

レーザ・アークハイブリッド溶接によりビードオンプレート溶接施工した時の母材の熱履歴を測定すると共に，入熱効率を未知変数とする最適化問題として取り扱い，高い探索性能が報告されている実数値GAである親子間完全世代交代モデルJGG及び多親交叉REXを用いて入熱効率を同定した．

Language：Japanese   Publishing type：Research paper (other academic)  

造船所における切断工程で多用されているプラズマ切断及びガス切断により開先加工された鋼板を用い，ハイブリッド溶接により製作した継手に対しビッカース硬さ試験や断面マクロ観察等の継手評価を実施することで，継手品質に及ぼす接合面性状の影響を調査した．

Language：Japanese   Publishing type：Research paper (other academic)  

Investigation on Wear Estimation Method for Mooring Chain of Floating Structures，
Takaaki Takeuchi, Kimihiro Toh, Tomoaki Utsunomiya and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.27, 2017S-GS21-5, pp.789-793.

Language：Japanese   Publishing type：Research paper (other academic)  

A Study on Fabrication Accuracy of Hull Blocks by using Three Dimensional Scanner，
Yasutaka Kobayashi, Eiji Date, Syuzou Kaneshiro, Keisuke Nara, Fumito Ujino, Hisao Narimatsu, Kazuhiro Hirao, Takeshi Koide, Shogo Uno, Kazuhiko Kumagawa, Yasuhiro Kawamoto, Hideo Shirazawa and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.27, 2017S-OS5-7, pp.209-211.

Language：Japanese   Publishing type：Research paper (other academic)  

Trend of the Joint Industrial Research Project on Laser-Arc Hybrid Welding Applied to the Hull Construction stages in Japan
Koji GOTOH, Ryuhei TAKESHITA, Shuichi TSUMURA, Hisao NARIMATSU and Issei UCHINO
Proceedings of the 86th Laser Materials Processing Conference, pp.13-19, December 2016.

Repository Public URL： http://hdl.handle.net/2324/4794467

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack Propagation Considering Crack Closure over Initial Crack Surfaces under Excessive Compressive Loading，
Yoshifumi Takaki and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.23, 2016A-OS4-7, pp.131-136.

Language：Japanese   Publishing type：Research paper (other academic)  

Preliminary Investigation on Wear Performance for Mooring Chain Applied to Floating Wind Turbine，
Koji Gotoh, Koji Murakami, Masataka Nakagawa and Tomoaki Utsunomiya,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.23, 2016A-GS27-3, pp.587-592.

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack Propagation in an Out-of-plane Gusset Welded Joints under Biaxial Tensile Loadings with Different Phases，
Keishi Shimizu, Koji Gotoh, Yosuke Anai and Toshio Niwa,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.23, 2016A-GS7-3, pp.247-252.

Language：English   Publishing type：Research paper (international conference proceedings)  

Most of in-service welded built-up structures, which contain many welded joints as fatigue crack initiation sites, are subjected to many types of loading and these loadings have different axial components with different phases. However, the structural integrities are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition. Most of these codes are based on the S-N curves approach.
On the other hand, some of authors proposed the numerical simulation method of fatigue crack propagation histories of a cracked plate subjected biaxial loadings with phase difference of each loading component.
In this study, numerical simulation of fatigue crack propagation in an out-of-plane gusset welded joint under biaxial loading with two different phase conditions were performed. Estimated fatigue crack propagation histories were compared with measured crack evolution for verification of our method.

Language：English   Publishing type：Research paper (international conference proceedings)  

To spread the wind power generation plant on offshore over the world, the floating wind turbine facility which is installed in the deep sea area is essential. One of the issues related to the practical application of the commercial level of the facility installed in the deep sea is the reduction of a mooring cost. Breaking the mooring chain in the floating wind turbine facility installed in the deep sea area by progressing the wear will lead to enormous damage. Therefore, it is necessary to establish a quantitative wear evaluation method for mooring chains. In this study, the experimental facility to reproduce the wearing phenomena in actual scale mooring chains due to the motion of floating body caused by waves was constructed and confirmed the usefulness of our developed machine. Besides, the numerical simulation to estimate the amount of wear was attempted by using the finite element analysis with measured wear characteristics of applied material.

Repository Public URL： http://hdl.handle.net/2324/4794458

Language：Japanese   Publishing type：Research paper (other academic)  

位相差を有する二軸引張載荷を受ける面外ガセット溶接継手を対象に，著者らが提案した二軸載荷問題を近似的に単軸載荷問題に置き換える手法と，Toyosadaらによる等価分布応力法を用いた任意形状を有する亀裂材に対する疲労亀裂成長履歴の予測方法を活用することで，同継手における疲労亀裂成長履歴を推定した．

Language：Japanese   Publishing type：Research paper (other academic)  

アルミニウム合金A6N01，難燃性マグネシウム合金AZX611及びそれぞれのFSW 継手の10^8回レベルまでの疲労強度を比較的短時間かつ，従来の試験方法に沿って実施可能な，片持ち梁式回転曲げ疲労試験機1)を用いて疲労強度評価を実施し，表面粗さの影響，小野式回転曲げ疲労試験及び軸疲労試験の試験結果との比較，母材とFSW継手の疲労強度比較を実施した．

Language：Japanese   Publishing type：Research paper (other academic)  

初期亀裂面が接触する場合にも対応できるように亀裂開閉口モデル拡張し，平均応力の低い荷重条件, 平均応力が変動する条件, 航行中の船舶のホイッピング荷重履歴を模擬した荷重条件等において疲労亀裂伝播解析を実施し，実測結果との比較を行った．

Language：Japanese   Publishing type：Research paper (other academic)  

レーザ・アークハイブリッド溶接施工におけるルートギャップ裕度を広げるべく，サブマージアーク溶接では既知の工法であるセラミック製裏当て材と開先充填材（メタルパウダー）を，レーザ・アークハイブリッド溶接による突合せ継手製作に適用する新施工法の確立を目指し，実現性の評価及び課題抽出を行った．

Language：English   Publishing type：Research paper (international conference proceedings)  

Expansion of the application of aluminium alloy A6005C and uninflammable magnesium alloy AZX611 for railway vehicle is expected to reduce the total weight for suppressing the driving energy.
To achieve this objection, assurance of the structural integrity, in particular the fatigue performance of these alloys and their joints fabricated by FSW is essential.
FSW is a novel joining technology methods for light metals and has advantages comparing with standard arc welding applied for railway vehicle constructions.
Fatigue performance of A6005C and AZX611 and their FSW joints investigated by high speed cantilever type rotating tests and axial fatigue tests are reported in this paper.
Some topics for fatigue test, which correspond to the effect of specimen surface roughness, the temperature elevation effect in high speed rotating test and the difference loading mode, are discussed.

Repository Public URL： http://hdl.handle.net/2324/4794432

Language：Japanese   Publishing type：Research paper (other academic)  

Residual stress of full penetration tee joints fabricated by laser-arc hybrid welding,
Ryuhei Takeshita, Shuichi Tsumura, Koji Murakami, Koji Gotoh and Seiichrio Tsutsumi,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers

Language：Japanese   Publishing type：Research paper (other academic)  

A Study on the Strip Yield Model for a Surface Crack,
Kohei Yamashita and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.22, May 2016, pp.433-438, (Paper ID: 2016S-GS5-2)

Language：Japanese   Publishing type：Research paper (other academic)  

A Study on The Usefulness of Laser Tack Welding for Laser/arc Hybrid Welding,
Shuichi Tsumura, Ryota Aoyagi and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.21, November 2015, pp.408-408, (Paper ID: 2015A-GS10-1)

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack Propagation Using Elastic-plastic Finite Element Analysis and a Proposal of Fatigue Crack,
Kohei Yamashita and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.21, November 2015, pp.369-374, (Paper ID: 2015A-GS8-1)

Language：Japanese   Publishing type：Research paper (other academic)  

Demonstration on Cost-reduction of Mooring System for Floating Offshore Wind Turbine Facility,
Tomoaki Utsunomiya, Koji Gotoh, Katsutoshi Kita, Osamu Kobayashi, Iku Sato, Hirofumi Takano and Toshiya Iwashita,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.21, November 2015, pp.265-266, (Paper ID: 2015A-GS3-4)

Language：English   Publishing type：Research paper (international conference proceedings)  

Overview of the education program, Engineering Leaders English Program (ELEP) in School of Engineering in Kyushu University is briefly introduced. ELEP was established to enhance the globalization and to cultivate the entrepreneurship of Japanese students, especially from the viewpoint of science and engineering fields. Customized English training program and the exercises of startup proposal are provided to achieve the objective of this program.

Language：English   Publishing type：Research paper (international conference proceedings)  

Fatigue failures have sometimes taken place in weld joints due to stress concentration and tensile residual stress at the weld toe.
Therefore managements of fatigue crack initiation and propagation contribute to the enhancement of the fatigue life of welded steel structures.
The hammer peening process is well known as one of methods to improve the fatigue life of weld joints by generating the compressive residual stress field near the weld toe where recognized as the fatigue crack initiation site.
With respect to the fatigue life estimation of the welded steel structure which applied the compressive residual stress field near the weld toe, it is important not only fatigue life estimation for the fatigue crack initiation but also that for the fatigue crack propagation.
However there is few research work which deal with the fatigue crack estimation in the compressive residual stress field.
In this study, mechanism of fatigue crack propagation in the compressive residual stress field was clarified by experimental observation of crack propagation from a surface crack after hammer peening. Morphology of a propagating surface crack in plate and gusset weld joint specimens were measured by the beach mark method.
As a result, it was clarified that morphology of surface crack propagated in the compressive residual stress field was different from that in neutral stress filed.
And this phenomenon was clearly observed especially under the low stress intensity factor condition.

Language：Japanese   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (other academic)  

近年，船舶・海洋構造物の構造健全性評価に関し，複数周波数成分が重畳した載荷履歴条件下における疲労強度評価の必要性が指摘され，これに関する研究が数多く実施されているが，多くの場合はS-N曲線と線形累積損傷側に基づく方法であり，疲労亀裂発生挙動を定量的に検討した事例は著者らの知る限りでは報告されていない．
本報告では，著者の一部らが重畳応力履歴条件下における疲労亀裂伝播挙動に関して亀裂伝播に有効に寄与する応力成分の抽出方法を，豊貞らにより提案された無亀裂状態から第一結晶粒界に到達するまでの間の微視疲労亀裂の成長挙動評価手法を組み合わせることで，重畳応力履歴条件下における疲労亀裂発生挙動を検討した結果について紹介する．

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Study on the angular distortion in Tee type full penetrated welded joint fabricated by
the laser/arc hybrid welding,
Shuichi TSUMURA，Koji MURAKAMI，Koji GOTOH,
Quarterly Journal of the Japan Welding Society Vol. 33　No. 2　2015, pp.194-201.

DOI： http://doi.org/10.2207/qjjws.33.194

Repository Public URL： http://hdl.handle.net/2324/4794430

Language：Japanese   Publishing type：Research paper (other academic)  

Fatigue Strength of Laser-arc Hybrid Welded T-joint under Full Penetration Welding ,
Shuichi Tsumura, Koji Murakami and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.20, May 2015, pp.513-516, (Paper ID: 2015S-GS21-3)

Language：Japanese   Publishing type：Research paper (other academic)  

A study on Fatigue Crack Growth of a Surface Crack,
Yosuke Anai, Toshio Niwa, Shota Ejima and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.20, May 2015, pp.501-504, (Paper ID: 2015S-GS20-4)

Language：Japanese   Publishing type：Research paper (other academic)  

Effect of Compressive Residual Stress on Fatigue Crack Propagation ,
Yasushi Morikage, Satoshi Igi, Kenji Oi, Yuichiro Jo, Koji Murakami and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.20, May 2015, pp.493-496, (Paper ID: 2015S-GS20-2)

Language：Japanese   Publishing type：Research paper (other academic)  

A Study of Replacing Method to the Single-Frequency Stress History to the Superimposed Stress History with Multiple Frequency Components ,
Kazuki Matsuda and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.20, May 2015, pp.489-492, (Paper ID: 2015S-GS20-1)

Language：Japanese   Publishing type：Research paper (other academic)  

Study on relationship between angular distortion of T-joint welded by laser/arc hybrid welding and heat input parameter,
Shuichi TSUMURA, Koji MURAKAMI and Koji GOTOH,

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack Propagation under Various Loading Condition by Using Equivalent Fatigue Stress Range Method,
Kazuki MATSUDA and Koji GOTOH,

Language：Japanese   Publishing type：Research paper (other academic)  

A Suggestion for Checking Items on Fatigue Damage Reports,
Toichi Fukasawa, Naoki Osawa, Koji Gotoh and Yoshitaka Ogawa,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.19, November 2014, pp.31-32, (Paper ID: 2014A-OS1-6)

Language：Japanese   Publishing type：Research paper (other academic)  

A review of fatigue strength evaluation in the superimposed stress history conditions,
Naoki Osawa, Koji Gotoh and Tetsuya Nakamura,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.19, November 2014, pp.27-29, (Paper ID: 2014A-OS1-5)

Language：Japanese   Publishing type：Research paper (other academic)  

Fatigue strength of non-load carrying type Tee welded joints with large gap,
Jun-ichi Deguchi and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.19, November 2014, pp.255-258, (Paper ID: 2014A-GS4-6)

Language：English   Publishing type：Research paper (international conference proceedings)  

Fatigue crack propagation behavior under superposed loading histories which have various mean stresses is highlighted. Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Re-tensile Plastic zone Generating) load criterion for fatigue crack propagation is improved to enable the extraction of the effective loading history. The critical value of the plastic hysteresis for the stress versus strain relationship occurring in the vicinity of a crack tip is defined as the control parameter for extracting the effective loading history. Fatigue crack propagation tests under various superimposed loading conditions were performed and comparison of fatigue crack propagation curves obtained from the improved numerical simulations, with the measurements is performed. These comparisons show the validity of the proposed procedure for extracting the effective loading history from the superposed loading history containing different frequencies. Subsequently, traditional cumulative fatigue damage evaluation is conducted and consider the tendency of fatigue damage value affected by mean stresses.

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (international conference proceedings)  

In ship hull design, longitudinal stiffeners may be twisted or knuckled to keep the continuity of strength along the vessel.
This occurs at angled discontinuities such as discontinuous connections at the transverse web between two longitudinal stiffeners having different angles, e.g., a side shell longitudinal stiffener in the rounded part of the ship’s hull.
Although the criteria for selection of “twist”, “knuckle”, or “angled discontinuity” as it is should be strength criteria, there are no generalized criteria or published systematic studies, and ship hull designers usually depend on experimental rules.
In this study we evaluate and compare the stress magnification factors and define the relative ratio between the stresses in the discontinuity and continuity structures by using finite element analysis from a strength-of-materials point of view.
Our results show that under lateral load conditions the stress factor is larger in the twist structure than in the angled discontinuity structure, although under axial load conditions the stress factor in the knuckle and angle discontinuity structures is larger than in the twist structure.
Additionally, we propose a formula that estimates the factor in the knuckle structure based on the strength-of-materials approach.

Language：English   Publishing type：Research paper (international conference proceedings)  

This paper presents an improved simulation procedure for fatigue crack growth based on the strip yield model with a weight function.
The authors developed the numerical simulation model of fatigue crack growth by considering the strain hardening effect of materials using the modified strip yield model.
Numerical simulations of fatigue crack growth under many types of loading are performed to investigate the validity of our new proposed model.
Comparison of proposed simulation results with previous results and with experimental measurements confirms the superiority of the proposed method.

Language：English   Publishing type：Research paper (international conference proceedings)  

In the present study, the fatigue performance of the welded joint made by CO2 gas shielded welding with different gap sizes is investigated to obtain one of the supporting materials to modify the construction quality standards.
Allowable limits on the gap size of welded joints is specified in many construction quality standards based on experimental and empirical results from the welded joints made by manual metal arc welding.
The fatigue test results for the welded specimen with gap presents higher performance compared to the fatigue design S-N curves proposed by the International Institute of Welding (IIW).

Language：Japanese   Publishing type：Research paper (other academic)  

The Strip Yield Model and Numerical Simulation of Fatigue Crack Growth of Surface Crack,
Kohei Yamashita, Shota Ejima and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.18, May 2014, pp.105-108, (Paper ID: 2014S-S1-4)

Language：Japanese   Publishing type：Research paper (other academic)  

A study on the Scattering of Fatigue Crack Propagation Law based on the RPG Stress Criterion of the Structural Steel,
Kohei Yamashita and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.18, May 2014, pp.481-484, (Paper ID: 2014S-GS11-6)

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical simulation of fatigue crack propagation under superimposed loading histories
-(Part 2) Effect of variation in stress amplitude and mean stress for fatigue crack propagation -,
Kazuki Matsuda, Koji Murakami and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.18, May 2014, pp.463-466, (Paper ID: 2014S-GS11-1)

Language：Japanese   Publishing type：Research paper (scientific journal)  

Effect of Longitudinal Discontinuity on Stress Distribution Near the Connection Point of Longitudinal Stiffener and Transverse Web,
Shuichi Yamatoki, Seitaro Arimatsu and Koji Gotoh
Journal of the Japan Society of Naval Architects and Ocean Engineers,
Vol.18, 2013, pp.207-215.

Other Link： https://www.jstage.jst.go.jp/browse/jjasnaoe/18/0/_contents

Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue Crack Propagation under Biaxial Cyclic Loading Condition Containing Phase
Differences,
Koji GOTOH, Tohsio NIWA, Yosuke ANAI, Tetsuya OMORI and Yoshihisa TANAKA
Journal of the Japan Society of Naval Architects and Ocean Engineers,
Vol.18, 2013, pp.101-108.

Other Link： https://www.jstage.jst.go.jp/browse/jjasnaoe/18/0/_contents

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical simulation of fatigue crack propagation and crack opening and closing model considering the strain hardening effect of materials,
Kohei Yamashita and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.17, November 2013, pp.73-76, (Paper ID: 2013A-GS3-3)

Language：Japanese   Publishing type：Research paper (other academic)  

Fatigue crack growth behaviour of welded built-up structures under block program fatigue test,
Masao Takuno, Koichi Okada, Sadaharu Kusuba and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.17, November 2013, pp.41-44, (Paper ID: 2013A-GS1-2)

Language：English   Publishing type：Research paper (other academic)  

Numerical Study of Fatigue Performance of Butt Welded Joint with U and V-notch Undercut,
Ezzarhan Abdullah and Koji Gotoh,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.17, November 2013, pp.49-52, (Paper ID: 2013A-GS1-4)

Language：English   Publishing type：Research paper (international conference proceedings)  

Comparison of Hull Construction Quality Standards,
Koji GOTOH and Kazuhiro AOYAMA,
Proceedings of 12th International Symposium of Practical Design of Ships and Other Floating Structures (PRADS 2013),
2013, Volume I, pp. 94-101.

Language：Japanese   Publishing type：Research paper (other academic)  

著者らのグループでは，豊貞らが提唱したRPG荷重基準に基づく疲労亀裂伝播解析手法を実装した，疲労亀裂開閉口シミュレーションを構築し，種々の荷重履歴下における，同手法の妥当性を検証してきた．しかしながら，過大な荷重履歴変動を生じるブロック荷重履歴条件やスパイク荷重履歴条件における解析結果は，実測された伝播履歴と比べて過大な遅延現象を与えている．この理由として，従来の数値シミュレーションでは材料を弾完全塑性体としてモデル化し，材料の加工硬化現象を無視したため，疲労亀裂伝播に伴い亀裂面に取り込まれるcrack wake（残留引張変形層）が過大に評価され，その結果として亀裂が閉じやすくなるため，伝播挙動の遅延が過大になると推察された．
本研究では，材料の加工硬化現象を考慮できるように改善した亀裂結合力モデルを，疲労亀裂開閉口シミュレーションに実装することで，変動荷重履歴条件下での疲労き裂伝播挙動推定精度の向上を試みた結果を報告する．

Language：English   Publishing type：Research paper (international conference proceedings)  

In the ship-hull design phase, the distance of a misalignment of a cruciform welded joint is enlarged, by up to 100 mm for example, until its effect is thought to be inimized.
To control tolerance, we used a technique to estimate the coefficient of the misalignment effect: the ratio of the stress with misalignment to stress without misalignment. Current methods, created using the two-dimensional (2D) misalignment model and focusing on small misalignments, cannot be applied in the design phase. Misalignment models are needed, as there have been no studies of these joints and it is impractical to do finite element (FE) analysis in each case. We propose an estimation method of the coefficient of misalignment effect in three dimensions (3D). First, we created a new equation to estimate the coefficient in 2D. The equation accommodates larger misalignments. Second, we found the membrane component of a misaligned member stress is reduced as a 3D effect and the coefficient converges given a certain
misalignment value. Third, a modified equation taking the effect into account indicates the coefficient in 3D.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Numerical Simulation of Fatigue Crack Propagation under Variable Amplitude Loading
Containing Two Different Frequency Components
Koji GOTOH and Kazuki Matsuda,
Journal of the Japan Society of Naval Architects and Ocean Engineers,
Vol.17, 2013, pp.75-81

Other Link： https://www.jstage.jst.go.jp/browse/jjasnaoe/17/0/_contents

Language：Japanese   Publishing type：Research paper (scientific journal)  

Improved Point Load Weight Function for Stress Intensity Factor of a Surface and an
Embedded Crack
Koji GOTOH and Tetsuya Otagro,
Journal of the Japan Society of Naval Architects and Ocean Engineers,
Vol.17, 2013, pp.65-73

Other Link： https://www.jstage.jst.go.jp/browse/jjasnaoe/17/0/_contents

Language：English   Publishing type：Research paper (other academic)  

Practical Formula of Stress Concentration Factor for Butt Welded Joint with Undercut,
Ezzarhan Abdullah and Koji GOTOH,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.16, May 2013, pp.531-534, (Paper ID: 2013S-GS6-11)

Language：Japanese   Publishing type：Research paper (scientific journal)  

A crystal plasticity FE analysis is conducted to understand the fatigue phenomena subjected to cyclic stresses.
For simplicity,　the crystal plasticity model assumes an isotropic hardening/softening and an isotopic elasticity.
The effects of inclusions with the　varieties of positions and mechanical properties on the initiation and accumulation of local-plastic strain at the stress level lower
than the dominant yielding stress state, i.e macroscopically elastic condition, are discussed in detail.

Language：Japanese   Publishing type：Research paper (other academic)  

Effect of the Geometry on Stress Variation in a Knuckle Model,
Shuichi YAMATOKI and Koji GOTOH,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.16, May 2013, pp.501-504, (Paper ID: 2013S-GS6-3)

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack under Superposed Loading Histories
–Mean Stress Effect for Fatigue Crack Propagation-,
Kazuki MATSUDA, Koji MURAKAMI, Koki SUGINO and Koji GOTOH,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.16, May 2013, pp.523-526, (Paper ID: 2013S-GS6-9)

Language：Japanese   Publishing type：Research paper (other academic)  

Static Strength Evaluation of the Side-fillet Welded Joint by FE Analysis,
Shuichi TSUMURA and Koji GOTOH,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.16, May 2013, pp.167-170, (Paper ID: 2013S-YS2-4)

Language：English   Publishing type：Research paper (scientific journal)  

Fracture control of extremely thick welded steel plates applied to the deck structure of large container ships
Sumi, Yoichi; Yajima, Hiroshi; Toyosada, Masahiro; Yoshikawa, Takao; Aihara, Shuji; Gotoh, Koji; Ogawa, Yoshitaka; Matsumoto, Toshiyuki; Hirota, Kazuhiro; Hirasawa, Hideyuki; Toyoda, Masanobu; Morikage, Yasushi
JOURNAL OF MARINE SCIENCE AND TECHNOLOGY, Vol.18, No.4, 2013, pp.497-514.

DOI： 10.1007/s00773-013-0222-5

Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue strength of austenitic stainless steels applied to chemical tankers
Hideyuki Uchimura, Masao Takuno, Koji Murakami, Koji Gotoh
Journal of the Japan Society of Naval Architects and Ocean Engineers, Vol.16, December 2012, pp.89-97.

Other Link： https://www.jstage.jst.go.jp/article/jjasnaoe/16/0/16_89/_article

Language：Japanese   Publishing type：Research paper (other academic)  

Estimation of Stress Increase Ratio Caused by Misalignment,
Shuichi YAMATOKI, Seitaro ARIMATSU and Koji GOTOH,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.15, November 2012, pp.495-498, (Paper ID: 2012A-GS25-3)

Language：Japanese   Publishing type：Research paper (other academic)  

A Study of Determination procedure of the fatigue crack growth threshold ΔKth,
Koji MURAKAMI and Koji GOTOH
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.15, November 2012, pp.143-146, (Paper ID: 2012A-GS3-2)

Language：Japanese   Publishing type：Research paper (other academic)  

Experimental investigation of the fatigue crack growth behavior from the shearing mode to the opening mode,
Kazuki MATSUDA, Ryutaro TSUJI, Koji MURAKAMI and Koji GOTOH
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.15, November 2012, pp.147-150, (Paper ID: 2012A-GS3-3)

Language：Japanese   Publishing type：Research paper (other academic)  

Fatigue crack growth behaviour under bi-axial loading condition
-Effect of phase difference (1st report)-,
Koji GOTOH, Toshio NIWA, Yosuke ANAI, Tetsuya OMORI and Yoshihisa TANAKA.
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.15, November 2012, pp.159-162, (Paper ID: 2012A-GS4-2)

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical simulation of fatigue crack propagation considering the strain hardening effect of materials,
Kohei YAMASHITA, Kazuki MATSUDA and Koji GOTOH.
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.15, November 2012, pp.171-174, (Paper ID: 2012A-GS4-5)

Language：Japanese   Publishing type：Research paper (other academic)  

Improvement of estimation procedure of the stress-strain relation under arbitrary strain rate and temperature conditions,
Koji GOTOH and Naoki AKAHOSHI.
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.15, November 2012, pp.463-466, (Paper ID: 2012A-GS24-1)

Language：Japanese   Publishing type：Research paper (other academic)  

Estimation of Stress Increase Ratio Caused by Misalignment,
Shuichi YAMATOKI, Seitaro ARIMATSU and Koji GOTOH,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.15, November 2012, pp.491-494, (Paper ID: 2012A-GS25-2)

Language：English   Publishing type：Research paper (international conference proceedings)  

Multiple criteria concerning the misalignment of cruciform welded joints have been published and usually applied in ship-hull construction.
These criteria only adopt a 2D model with axial load and generally do not consider the thickness of intercalated members.
These are thought to be inapplicable to joints for which the misalignment is much larger than the thickness of a member.
First, the authors investigate the way of stress increases by finite element (FE) analysis, and propose a new equation for strength-of-materials.
Their results are in excellent agreement, thus validating the reliability of the equation in estimating stress variation from a misalignment.
Second, 3D FE analyses of both the shell element and the solid element are described.
By comparing the analytical results for both elements, the shell element is found to apply in misalignment analysis.
Finally, by FE analyses of the shell element, the intercalated plate thickness is found to affect stress and the stress converges because of misalignment.

Language：English   Publishing type：Research paper (international conference proceedings)  

This paper presents an improved numerical simulation procedure for fatigue crack growth based on the strip yield model with a weight function.
In the previous numerical model, one-dimensional bar elements plugged up the chink corresponding to the virtual crack opening displacement in the plastic zone to describe the crack wake over fatigue crack surfaces.
However, this numerical simulation method gives poor growth estimations under large variable loading histories, e.g. spike overloading.
It is possible that insufficient consideration of the strain hardening effect of materials leads to excess crack closure.
The authors develop the numerical simulation model of fatigue crack growth by considering the strain hardening effect of materials using the modified strip yield model.
Numerical simulations of fatigue crack growth under many types of loading are performed to investigate the validity of our new proposed model.
Comparison of proposed simulation results with previous results and with experimental measurements confirms the superiority of the proposed method.

Language：English   Publishing type：Research paper (international conference proceedings)  

It is well known that the strength capacity of the side fillet welded joints loses as its weld length becomes longer.
An analytic expression of the stress distribution over the throat section along weld length was given by Troelsch.
His expression indicates that the stress along weld length shows peak values at both weld ends and decreases toward the mid position of weld length and that the weld bead except both end portions has little contribution as the load carrying components.
Then, it is conducted that prolonging the weld length of side fillet welded joints is meaningless to improve the structural integrity of the joints.
However, the effect of geometrical conditions, e.g. the size of leg length of fillet weld or dimensions of width and breadth of straps, was not considered in Troelsch’s expression.
Authors carried out some finite element calculations to investigate the effect of geometrical conditions on the mechanical behavior of the side fillet welded joints.
Comparison FE results of the stress distribution over the throat section along weld length with ones obtained by Troelsch’s analytical expression.
These comparisons conduct that the allowable geometrical condition of Troelsch’s expression and some knowledge of the mechanical behavior of the side fillet welded joints.

Language：Japanese   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (other academic)  

Effect of the Loading Mode and the Thickness of Intercalated Plate on the Strength Degradation caused by the Misalignment (2nd report),
Syuichi YAMATOKI, Seitaro ARIMATSU and Koji GOTOH
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.14, May 2012, pp.175-178, (Paper ID: 2012S-G1-8)

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack Propagation Under Superimposed Variable Amplitude Loading,
Koji GOTOH and Kazuki MATSUDA
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.14, May 2012, pp.17-20, (Paper ID: 2012S-OS1-5)

Language：Japanese   Publishing type：Research paper (other academic)  

Practical point load weight function for stress intensity factor of a surface and an embedded crack,
Koji GOTOH and Tetsuya OTAGURO
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.14, May 2012, pp.167-170, (Paper ID: 2012S-G1-6)

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Life for Cruciform Joint Applied to Stainless Chemical Tankers,
Hideyuki UCHIMURA, Masao TAKUNO and Koji GOTOH,
Proceedings of Welding Structure Symposium by the Japan Welding Society, November 2011, pp.403-406.

Language：Japanese   Publishing type：Research paper (other academic)  

Fatigue Strength of Load-Carrying Type Cruciform Joint of Stainless Chemical tankers.
Hideyuki UCHIMURA, Isshin FUJII and Koji GOTOH,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.13, November 2011, pp.59-60, (Paper ID: 2011W-G2-3)

Language：Japanese   Publishing type：Research paper (other academic)  

Effect of the loading mode and the transverse frame thickness on the strength degradation caused by the misalignment,
Shuichi YAMATOKI, Seitaro ARIMATSU and Koji GOTOH,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.13, November 2011, pp.65-66, (Paper ID: 2011W-G2-3)

Language：Japanese   Publishing type：Research paper (other academic)  

A proposal of the effective hull construction quality control method by applying the risk assessment system,
Hiromitsu TSUGAWA, Kei MANABE, Yasuyuki ENAMI, Yuzo NAKAYAMA, Sadanobu MACHIDA, Yasuhiro IZUMI, Shinji KAWANO and Koji GOTOH,
Conference Proceedings, The Japan Society of Naval Architects and Ocean Engineers,
Vol.13, November 2011, pp.95-98, (Paper ID: 2011W-G2-14)

Language：Japanese   Publishing type：Research paper (other academic)  

Analysis on softening behavior under macroscopically-elastic cyclic loading condition,
Seiichiro TSUTSUMI, Naoyuki YAMATO, Koji GOTOH and Fionn DUNNE,
Proceedings of Welding Structure Symposium by the Japan Welding Society, November 2011, pp.381-386.

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

A Conventional Growth Estimation Formula of the Representative Surface Crack Replacing Plural Surface Cracks Generated at the Sound Stress Concentration Site,
Yosuke ANAI, Koji MURAKAMI and Koji GOTOH,
Proceddings of International Conference on Advanced Technology in Experimental Mechanics 2011 (ATEM'11), OS14F029, September, 2011

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4763157

Language：Japanese   Publishing type：Research paper (other academic)  

Fundamental study of the length of Electric Fusion socket type joint applied to the city gas pipeline
Daichi MIYAMOTO and Koji GOTOH，
Proceedings of Japan Welding Society, Kyushu-chapter, No.8, 2011, pp.41-44

Language：Japanese   Publishing type：Research paper (other academic)  

Verification of the fatigue crack nucleation model based on the RPG (Re-tensile Plastic zone Generating) load criterion,
Kazuki MATSUDA, Koji MURAKAMI and Koji GOTOH，
Proceedings of Japan Welding Society, Kyushu-chapter, No.8, 2011, pp.37-40

Language：Japanese   Publishing type：Research paper (other academic)  

A Conventional Growth Estimation Method of Plural Surface Cracks Generated at Stress Concentration Sites
- Application into Wide Fatigue Cracks Initiation Sites -
Yosuke ANAI, Koji MURAKAMI and Koji GOTOH,
Conference Proceedings of the Japan Society of Naval Architects and Ocean Engineers, Vol.12, May 2011, pp.293-296, Paper ID: 2011S-G4-1

Language：Japanese   Publishing type：Research paper (other academic)  

Crystal plasticity FE analysis on initiation and accumulation of plastic strain under fatigue condition
Seiichiro TSUTSUMI, Naoyuki YAMATO, Koji GOTOH and Fionn DUNNE
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vol.11, pp.473-476, Paper ID:2010K-G10-1 November 2010

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack Propagation under Superimposed Loading,
Koji GOTOH and Hirokazu TAKAHASHI,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers,
Volume 11, 2010, pp.71-72, Paper ID:2010W-G2-5

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack Propagation under Biaxial Cyclic Loading,
Koji GOTOH and Takeshi UIKE,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers,
Volume 11, 2010, pp.77-78, Paper ID:2010W-G2-7

Language：Japanese   Publishing type：Research paper (other academic)  

Investigation of Some Questions in the Standard Test Method for Measurement of Fatigue Crack Growth Rate ASTM-E647 by Numerical Fatigue Crack Growth Simulation,
Koji MURAKAMI, Masaru HASHIMOTO and Koji GOTOH,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers,
Volume 11, 2010, pp.79-82, Paper ID:2010W-G2-8

Language：Japanese   Publishing type：Research paper (other academic)  

Development of Strip Yield Model Considering Work Hardening of Materials,
Keisuke HARADA and Koji GOTOH,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers,
Volume 11, 2010, pp.83-86, Paper ID:2010W-G2-9

Language：Japanese   Publishing type：Research paper (other academic)  

Relation between Stress and Strain of High Density Polyethylene Applied to City Gas Pipeline Considering Strain Rate Effect,
Koji GOTOH and Naoki UJIHIRA,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers,
Volume 11, 2010, pp.87-90, Paper ID:2010W-G2-10

Language：Japanese   Publishing type：Research paper (other academic)  

Prediction of fatigue crack initiation under variable amplitude loadings based on cyclic plasticity model,
Seiichiro TSUTSUMI, Koji GOTOH and Fionn DUNNE,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers, Vol.11, pp.139-142, Paper ID:2010E-OS1-7 November 2010

Language：Japanese   Publishing type：Research paper (other academic)  

Investigation of some questions in the standard test method for measurement of fatigue crack growth rate ASTM-E647 by applying numerical simulation of fatigue crack growth,
Masaru HASHIMOTO, Koji MURAKAMI and Koji GOTOH，
Proceedings of Japan Welding Society, Kyushu-chapter, No.7, 2010, pp.37-40

Language：Japanese   Publishing type：Research paper (other academic)  

Analyses of the Fatigue Crack Growth and the Resultant Brittle Crack Inititation from Embedded Flaws in Butt Welded Joints of Extremely Thick Plates,
Koji GOTOH, Masahiro TOYOSADA, Yoichi SUMI, O Kitamura, Toshiyuki Matsumoto and Masanobu TOYODA
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers,
Volume 10, 2010, pp.295-298, Paper ID:2010S-OS11-3

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (other academic)  

Estimation of Shape Evolution of an Embedded Elliptical Fatigue Crack,
Keisuke HARADA,Koji GOTOH and Masahiro TOYOSADA
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers West chapter,
Volume 9W, 2009, pp.85-88, Paper ID:2009W-G2-2

Language：Japanese   Publishing type：Research paper (other academic)  

Identification Approach of Stress Intensity Factor Weight Function for an Embedded Crack and a Semielliptical Crack in Finite Plate Thickness Problems,
Hirokazu TAKAHASHI and Koji GOTOH,
Proceedings of Welded Built-up Structures Integrity Symposium 2009, Japan Welding Society, pp.597-600

Language：Japanese   Publishing type：Research paper (other academic)  

Crystal Plasticity FE Analysis on Initiation of Plastic Strain under Macroscopically Elastic Stress State,
Seiichiro TSUTSUMI, Naoyuki YAMATO,Koji GOTOH and Fionn Dunne
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers West chapter,
Volume 9W, 2009, pp.83-84, Paper ID:2009W-G2-1

Language：Japanese   Publishing type：Research paper (other academic)  

Characteristics of Crack Propagation in Aluminum Alloy A5038-O and A5083-H32 Series,
Koji GOTOH, Koji MURAKAMI, Yasuo NODA, Keiji AKIZUKI and Tutomu TAKIMOTO
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers,
Volume 8, 2009, pp.453-456, Paper ID:2009-G5-12

Language：Japanese   Publishing type：Research paper (other academic)  

Calculation Method of Crack Opening Displacement by using Strip Yield Model for an Embedded Elliptical Crack,
Yukinobu NAGATA and Koji GOTOH,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers,
Volume 8, 2009, pp.439-442, Paper ID:2009-G5-8

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack Propagation Considering Work Hardening Effect,
Koji GOTOH, Yukinobu NAGATA, Keisuke HARADA and Koji KADOWAKI
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers,
Volume 8, 2009, pp.449-452, Paper ID:2009-G5-11

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (other academic)  

Applicability Evaluation of Strip Yield Model for Three Dimensinoal Crack Problems,
Yukinobu NAGATA, Kunishige FUKUDOME and Koji GOTOH,
Conference Proceedings of The Japan Society of Naval Architects and Ocean Engineers,
Volume 7W, 2008, pp.55-58, Paper ID:2008W-G2-3

Language：Japanese   Publishing type：Research paper (scientific journal)  

Cyclic Stress-Strain Relationship during High Cycle Fatigue Process
Seiichiro TSUTSUMI, Koji MURAKAMI, Koji GOTOH and Masahiro TOYOSADA

Language：Japanese   Publishing type：Research paper (scientific journal)  

Cyclic Plasticity Phenomena under Macroscopically Elastic-High Cycle Fatigue Process
Seiichiro TSUTSUMI, Koji MURAKAMI, Koji GOTOH and Masahiro TOYOSADA

Language：Japanese   Publishing type：Research paper (other academic)  

Fundamental investigation of the extended strip yield model for notched materials
Koji GOTOH and Shinnosuke TSUTSUMI
Conference Proceedings of the Japan Society of Naval Architects and Ocean Engineers

Language：Japanese   Publishing type：Research paper (other academic)  

Stress Intensity Factors for Three Dimensional Cracks by Applying Slice Synthesis Methodology
Yukinobu NAGATA and Koji GOTOH
Conference Proceedings of the Japan Society of Naval Architects and Ocean Engineers

Language：English   Publishing type：Research paper (international conference proceedings)  

A practical estimation of welding deformation in the assembly stage of hull panel structures
Koji GOTOH, Ryohei KAWASHIMA and Masahiro TOYOSADA
Proceedings of International Conference of Computational and Experimental Engineering and Sciences 2008 (ICCES'08)

Repository Public URL： http://hdl.handle.net/2324/4785267

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (other academic)  

A practical estimation of welding deformation in the assemble stage of hull panel structures,
Koji GOTOH, Ryohei KAWASHIMA and Masahiro TOYOSADA,
Conference Proceedings of the Japan Society of Naval Architects and Ocean Engineering,
Vol.5W, November, 2007, pp.65-68

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Cyclic Plasticity Model with Damage
- Fatigue Crack Nucleation under Macroscopically Elastic Condition -

Language：Japanese   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (other academic)  

Estimation of Shape Development of a Surface Fatigue Crack,
Koji Gotoh, Yukinobu Nagata and Masahiro Toyosada,
Conference proceedings of the Japan Society of Naval Architects and Ocean Engineering, Vol.3 (May 2007), pp.429-432

Language：Japanese   Publishing type：Research paper (other academic)  

A Conventional Growth Estimation Method of Multiple Surface Cracks Generated by Fatigue in the stress concentration region,
Youske Anai, Koji Murakami, Koji Gotoh and Masahiro Toyosada,
Conference proceedings of the Japan Society of Naval Architects and Ocean Engineering, Vol.3 (November 2006), pp.383-386

Language：Japanese   Publishing type：Research paper (other academic)  

Fatigue Life Estimation for a Long Fatigue Crack in Large-scale Specimen in Imitation of Hull Skin Plate,
Koji Gotoh, Yukinobu Nagata and Masahiro Toyosada,
Conference proceedings of the Japan Society of Naval Architects and Ocean Engineering, Vol.3 (November 2006), pp.387-390

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (other academic)  

Fatigue Crack Growth in the First Grain Boundary Adjacent Notch Root

Language：Japanese   Publishing type：Research paper (other academic)  

Fatigue Crack Initiation and Propagation Analysis in the Hull Double Bottom Structural Model

Language：Japanese   Publishing type：Research paper (other academic)  

A Simple Estimation Method of The Stress Distribution Normal to Cross Section at Weld Toe in the Non-load Carrying Joints

Language：Japanese   Publishing type：Research paper (other academic)  

Physical Meaning of Fictitious COD at Notch Root

Language：Japanese   Publishing type：Research paper (other academic)  

Concepts of Equivalent Distributed Stress and Representative Surface Crack in FLARP

Language：Japanese   Publishing type：Research paper (other academic)  

Program to Foster Leaders in Fundamental Skills of Design / Production in industry-University Collaboration in Kyushu University: Welding Design Course,

Masahiro TOYOSADA, Koji GOTOH, Hiroshi FUJIMURA and Jyun-ichi HOJO,

Proceedings of Japan Society for Engineering Education,
pp.246-247, 2006

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4793198

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (other academic)  

Numerical Simulation of Fatigue Crack Growth for the In-plane Gusset Welded Joint

Language：Japanese   Publishing type：Research paper (other academic)  

Growth prediction of multiple fatigue surface cracks initiating from stress concentration region without initial defects - Stress ratio effect for the changing manner of aspect ratio of the Equivalent Surface Crack -，
Proceedings of Japan Welding Society, Kyushu chapter,
No.2, 2005, pp.11-19

Language：Japanese   Publishing type：Research paper (other academic)  

Fatigue crack growth prediction on in-plane gusset joint,
Proceedings of Japan Welding Society, Kyushu chapter,
No.2, 2005, pp.28-40

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Fatigue Damage at the Root of the Gate Lip of the Water Gate under Variable Water Pressure due to Tide and Ocean Wave

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (other academic)  

A fatigue life prolonging method for welded built-up steel structures by the grain fining around stress concentration regions,
Yukinobu NAGATA, Masahiro TOYOSADA, Koji GOTOH and Koji MURAKAMI,
Proceedings of Japan Welding Society, Kyushu-chapter,
No.1, pp.14-25

Language：Japanese   Publishing type：Research paper (other academic)  

A Study of the inelastic deformation under pricipal stress axes rotation -Effect of the non-coaxiality induced by anisotropy and tangential plasticity-,
Seichiro TSUTSUMI, Masahiro TOYOSADA, Koji GOTOH and Koichi HASHIGUCHI
Proceedings of Japan Welding Society, Kyushu-chapter,
No.1, pp.1-13

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4793196

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Simple Estimation Method of the Normal Stress over the Cross-Section of a Plate at Weld Toe,
Koji GOTOH, Keitaro KONUMA and Masahiro TOYOSADA
Journal of the Society of Naval Architects of Japan,
Vol.195,2004, pp.283-289

Repository Public URL： http://hdl.handle.net/2324/4794748

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10773-003-0152-9

Repository Public URL： http://hdl.handle.net/2324/4755282

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4752587

Language：Japanese   Publishing type：Research paper (scientific journal)  

Improvement of Constitutive Equation in Steel Considering the Effect of Strain Rate and Temperature,
Transactions of the West-Japan Society of Naval Architects, No.105

Language：Japanese   Publishing type：Research paper (scientific journal)  

Pysical meaning of the fictitious crack in Dugdale model,
Transactions of the West-Japan Society of Naval Architects, No.105

Language：Japanese   Publishing type：Research paper (other academic)  

A Proposal of Constitutive Equation Considering the Effect of Strain rate and Temperature,
Proceedings of Proceedings of Welded Built-up Structures Integrity Symposium 2002

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4752583

Language：Japanese   Publishing type：Research paper (scientific journal)  

Damage Analysis of a Fish Preserve Made of Aluminum Alloy,
Transactions of the West-Japan Society of Naval Architects, No.99

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Practical Estimation Method of the Skin Plate Distorsion Derived from Fillet Weld,
Journal of the Society of Naval Architects of Japan, Vol.189

Language：Japanese   Publishing type：Research paper (scientific journal)  

A Study of Crack Depth Effect and Scattering of Fracture Toughness in Three Point Bend COD Specimen,
Journal of the Society of Naval Architects of Japan, Vol.188

Language：Japanese   Publishing type：Research paper (scientific journal)  

Numerical Study on Fracture Resistance Performance of Beam-Ends in Steel Frames,
Journal of Structural Construction Engineering, AIJ, No.518,pp. 111-118

Language：Japanese   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Repository Public URL： http://hdl.handle.net/2324/4752591

Event date： 2015.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：産業技術総合研究所　臨海副都心センター   Country：Japan  

Koji GOTOH, Shuichi TSUMURA and Issei UCHINO;
Overview of the joint research project for introducing laser-arc hybrid welding in Japanese shipbuilding industries,
The 82nd Laser Materials Processing Conference,
National Institute of Advanced Industrial Science and Technology (AIST) Tokyo Waterfront,
January 2015.

Event date： 2014.6 - 2014.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Norwegian University of Science and Technology, Trondheim   Country：Norway  

Most of in-service welded built-up structures, which contain many welded joints as fatigue crack initiation sites, are subjected to many types of loading and these loadings have different axial components with different phases.
However, the structural integrities are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition. Most of these codes are based on the S-N curves approach.
On the other hand, authors proposed the numerical simulation method of fatigue crack propagation histories of a cracked plate subjected biaxial loadings with phase difference of each loading component.
Fracture mechanics approach is applied to establish our method. In this study, fatigue crack growth behaviour of an out-of-plane gusset welded joint under biaxial loading with two different phase conditions were investigated.
The phase difference effect for fatigue crack shape evolution under biaxial loading was confirmed by measured ones.
Besides, comparisons of measured crack evolution with the numerical simulation results were performed to validate of our fatigue crack growth simulation for welded joints.

Other Link： http://www.sciencedirect.com/science/article/pii/S2211812814002491

Event date： 2014.6

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco (Palace Hotel)   Country：United States  

Numerical simulations of fatigue crack growth of welded structural component were performed under fatigue testing conditions with block loading and constant stress range and the fatigue crack growth profiles were measured under the same loading conditions. In the experiments, fatigue cracks developed at the boxing fillet welded toe and grew toward the top flange plates of the specimens.
An advanced fracture mechanics approach based on the improved effective stress intensity factor range, which is the RPG (Re-tensile Plastic zone Generating) stress criterion, was applied to perform the numerical simulations of fatigue crack growth in the modeled components. A comparison of estimated fatigue crack growth profiles with measured ones verified that a reasonable estimation of fatigue crack growth can be estimated by applying the proposed numerical method.

Event date： 2013.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Nantes (La Cite Nantes Events Centre and Center des Expositions Nantes Metropole)   Country：France  

Fatigue crack propagation under biaxial tensile loading is highlighted in this study. Ships and offshore structures are subjected to many types of loading, e.g. wave induced forces, gravity, and inertia forces. Generally, these loadings have different axial components with different phases. However, the structural integrities of structures and vessels are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition.
Most of these codes are based on the S-N curves approach. An approach that does not use S-N curves has been favored by researchers, with the fracture mechanics approach preferred for evaluating the fatigue life of structures. An advanced fracture mechanics approach was developed based on the Re-tensile Plastic zone Generating (RPG) stress criterion for fatigue crack propagation. In this study, fatigue crack propagation tests under biaxial loading with four different phase conditions are performed and the effect of the phase difference under biaxial loading is evaluated. A numerical simulation method of fatigue crack propagation based on the RPG stress criterion under different biaxial loading phase conditions is presented and compared to measured data.

Event date： 2013.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Nantes (La Cite Nantes Events Centre and Center des Expositions Nantes Metropole)   Country：France  

Fatigue crack propagation behavior under simulated whipping loadings which contain two different frequency components is highlighted. Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Re-tensile Plastic zone Generating) stress criterion for fatigue crack propagation is improved to enable the extraction of the effective loading history. The critical value of the plastic hysteresis for the stress versus strain relationship occurring in the icinity of a crack tip is defined as the control parameter for extracting the effective loading history. Comparison of fatigue crack propagation curves obtained from the improved numerical simulations with the measurements which were conducted by Sumi (2010) is performed. These comparisons show the validity of the proposed procedure for extracting the effective loading history from the superposed loading history containing different frequencies. In addition, imperfection of the S-N curves approach, which corresponds to the combination of the linear cumulative damage law and the loading cycle count by the rain flow method, is conducted.

Event date： 2012.9

Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Fatigue crack propagation behaviour under superposed loading histories which contain two different frequency components is highlighted.
Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Re-tensile Plastic zone Generating) load criterion for fatigue crack propagation is improved to enable the extraction of the effective loading history.
The critical value of the plastic hysteresis for the stress versus strain relationship occurring in the vicinity of a crack tip is defined as the control parameter for extracting the effective loading history.
Comparison of fatigue crack propagation curves, obtained from the improved numerical simulations, with the measurements under the superposed loading
histories, is performed.
These comparisons show the validity of the proposed procedure for extracting the effective loading history from the superposed loading history containing different frequencies.

Event date： 2012.7

Presentation type：Oral presentation (general)  

Venue：Rio de Janeiro (Windsor Barra Hotel)   Country：Brazil  

This paper presents an improved numerical simulation procedure for fatigue crack growth based on the strip yield model with a weight function.
In the previous numerical model, one-dimensional bar elements plugged up the chink corresponding to the virtual crack opening displacement in the plastic zone to describe the crack wake over fatigue crack surfaces.
However, this numerical simulation method gives poor growth estimations under large variable loading histories, e.g. spike overloading.
It is possible that insufficient consideration of the strain hardening effect of materials leads to excess crack closure.
The authors develop the numerical simulation model of fatigue crack growth by considering the strain hardening effect of materials using the modified strip yield model.
Numerical simulations of fatigue crack growth under many types of loading are performed to investigate the validity of our new proposed model.
Comparison of proposed simulation results with previous results and with experimental measurements confirms the superiority of the proposed method.

Event date： 2011.6

Presentation type：Oral presentation (general)  

Venue：Rotterdam (Beurs World Trade Center)   Country：Netherlands  

Event date： 2010.9

Presentation type：Oral presentation (general)  

Venue：Rio Othon Palace Hotel, Rio de Janeiro   Country：Brazil  

Overview of Japanese Joint Research Project on Safety-Related Issue of Extremely Thick Steel Plate Applied to Large Container Ships

Yoich Sumi, Hiroshi Yajima, Masahiro Toyosada, Takao Yoshikawa, Shuji Aihara, Toshiyuki Matsumoto, Kazuhiro Hirota, Hideyuki Hirasawa, Masanobu Toyoda and Koji Gotoh

11th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2010)

Event date： 2010.6

Presentation type：Oral presentation (general)  

Venue：Shanghai   Country：China  

Event date： 2009.11 - 2009.12

Presentation type：Oral presentation (general)  

Venue：Garden Villa Kaohsiung, Kaohsiung   Country：Taiwan, Province of China  

Event date： 2009.7

Presentation type：Oral presentation (general)  

Venue：Ottawa   Country：Canada  

Improvement of Slice Synthesis Methodology to Estimate Stress Intensity Factor of an Embedded Crack in Finite body
Koji GOTOH and Yukinobu NAGATA
The 12th International Conference on Fracture (ICF 12)
Session T02-S3 Analytical Models

Event date： 2009.5 - 2009.6

Presentation type：Oral presentation (general)  

Venue：Honolulu, Hawaii   Country：United States  

Applicability Evaluation of the Weight Function Based Strip Yield Model for an Embedded Crack Problem
Koji GOTOH and Yukinobu NAGATA
The 28th International Conference on Offshore Mechanics and Arctic Engineering (OMAE 2009)
Session 3-6: Advances in Fracture, Fatigue and Sealing Analysis

Event date： 2008.7

Presentation type：Oral presentation (general)  

Venue：Vancouver (Sheraton Wall center hotel)   Country：Canada  

Stress Intensity Factors for Three Dimensional Cracks by Applying Slice Synthesis Methodology
Koji GOTOH and Yukinobu NAGATA
The Eighteenth (2008) International Offshore and Polar Engineering Conference (ISOPE 2008)

Presentation type：Oral presentation (general)  

Venue：Lisbon   Country：Portugal  

Presentation type：Oral presentation (general)  

Venue：San Diego, CA   Country：United States  

Country：United States  

Presentation type：Oral presentation (general)  

Venue：New Orleans,Louisiana   Country：United States  

Presentation type：Oral presentation (general)  

Venue：Houston,Texas   Country：United States  

Presentation type：Oral presentation (general)  

Venue：Honolulu, Hawaii   Country：United States  

Presentation type：Oral presentation (general)  

Venue：Honolulu, Hawaii   Country：United States  

Presentation type：Oral presentation (general)  

Venue：Oslo   Country：Norway  

Presentation type：Oral presentation (general)  

Venue：Calgary   Country：Canada  

Presentation type：Oral presentation (general)  

Venue：Turin   Country：Italy  

Physical Meaning of the Fictitious Crack Opening Displaecement in Dugdale Model

Presentation type：Oral presentation (general)  

Venue：Indian Institute Technology (IIT), Madras   Country：India  

A Comparative Study of Computational Models for Fatigue Crack Propagation

Presentation type：Oral presentation (general)  

Venue：Hamburg   Country：Germany  

A Simple Estimation Method of the Stress Distribution Normal to Cross Section at Weld Toe in non-load carrying welded joints

Event date： 2024.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡県   Country：Japan  

Repository Public URL： https://hdl.handle.net/2324/7325943

Event date： 2024.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡県   Country：Japan  

Repository Public URL： https://hdl.handle.net/2324/7325944

Event date： 2024.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡県   Country：Japan  

Event date： 2024.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Kure, Hiroshima   Country：Japan  

It is known that fatigue crack growth behavior is dominated by cyclic plastic behavior near the crack tip. The purpose of this study is to improve the accuracy of measuring the dimensions of the alternating plastic region, which is the region where tensile and compressive plastic deformation overlap near the crack tip, using digital image correlation (DIC) method. To measure the dimensions of the alternating plastic region, fatigue crack propagation tests were conducted under two stress ratios using compact specimen (C(T) in ASTM E399). Two methods were employed to print speckle-patterns on the specimen surface for strain field measurement using the DIC method as analytical markers: (1) sprayed on the specimen surface with white and black ink, and (2) 3% nital etching solution was applied. To measure the alternating plastic zone (ῶ) under cyclic loading conditions, a high-speed camera was used to capture the strain fields near the crack tip under cyclic loading. To determine the dimensions of the alternating plastic zone, strain fields obtained from the results of the DIC method were analyzed. The elasto-plastic FE analysis was conducted to compare the results with DIC measurement. As the results, good agreement has been obtained in the low stress ratio condition rather than high stress ratio condition with the FE analysis.

Repository Public URL： https://hdl.handle.net/2324/7325689

Event date： 2024.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Kure, Hiroshima   Country：Japan  

In the process of constructing the hull, additional anti-vibration measures are sometimes required during the commissioning phase after construction. However, the current process of installation involves welding, which results in paint burning and requires additional repair works to be painted. Therefore, the use of structural adhesives, which are a joining method that does not cause paint burning, is expected to replace welding.
In this study, as a basic study for the use of structural adhesives instead of welding for joining vibration isolation curling members, the joint strength under static three-point bending loading was compared with that of welded joints by experiments and finite element (FE) analysis. In these experiments, four types of specimens were prepared: an arc-welded joints (leg length of 5 mm) and three types of adhesives joints (adhesives thickness of 0.5 mm, 3 mm, and 5 mm) to not only compare welded joints with adhesives joints, but also to examine difference in strength due to the thickness of adhesives layer. The experimental results showed that all of the adhesives joints broke at lower loads than the arc-welded joints, but the adhesives joints also have sufficiently improved bending stiffness compared to the main plate alone and have not ruptured under the designed load. It was confirmed that the thinner the adhesives layer thickness, the greater bond strength. In the FE analysis, the interface region was defined in between steel and adhesives sections. It was confirmed that the elastic deformation before peeling could be simulated by applying appropriately material properties to each section. On the other hand, the adhesives modeling needs to be improved to estimate the peeling behavior and local strain distribution in vicinity of the adhesives part accurately.

Repository Public URL： https://hdl.handle.net/2324/7325690

Event date： 2024.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Kure, Hiroshima   Country：Japan  

Laser-arc hybrid welding (LAHW) can significantly reduce weld deformation due to the lower heat input compared to conventional arc welding, which is the standard method used in the current hull construction stages. Because of its superior heat concentration, LAHW has a relatively larger plate thicknesses over which I-shaped groove joints can be fabricated than conventional arc welding.
One of authors reported that one-pass welding without backing material was possible for a 17 mm thick steel plate with I-shaped groove. However, it was necessary to insert a filler gauge into the groove face and set the gap across the weld line to 0.5 mm.
From the viewpoint of introducing LAHW into the construction stage of general merchant ships, this study examined the welding work conditions to fabricate sound welded joints by LAHW under the following conditions: (1) groove fabrication by plasma cutting and (2) I-shaped groove with zero initial gap width. With reference to our previous studies, a search was conducted for welding parameters (laser power, arc current and voltage, etc.) that would allow the joint to be fabricated by a single pass of construction. As a result, although welding conditions with good bead appearance were identified, hot cracking of the weld metal occurred in some of the joints. To prevent hot cracking, the number of welding passes was changed from one to two, the length of the molten pool formed in the first pass was shortened in the thickness direction, and the second pass was performed by arc welding alone to compensate for the insufficient reinforcement height. As a result, it was possible to fabricate welded joints with good bead appearance without hot cracking.

Event date： 2024.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Kure, Hiroshima   Country：Japan  

This study explores the automation of welding inspection processes in shipyards by leveraging deep learning technologies to develop a system that aims to improve both efficiency and accuracy. We performed 90 horizontal fillet weld tests in a laboratory environment and 96 tests in a field environment on a T-shaped joint specimen, obtaining output logs from the welding machine during the welding process. We investigated deep learning computational methods and data preprocessing, introducing input data standardization and grid search for hyperparameters. As a result, the adjusted coefficient of determination for estimating leg length and undercut depth was improved. Next, we examined the frame size and the amount of frame shift for separating the input data were investigated, and the optimal values were identified that met practical criteria in a laboratory environment.
In addition, we conducted field tests using a simple welding carriage commonly used in shipyards to validate the applicability of our system in real-world environments. The results showed that the adjusted coefficients of determination for leg length and undercut depth estimation were 0.69 and 0.45, respectively, demonstrating the potential of our approach to improve production efficiency through automated weld quality inspection.
However, the study also identifies future challenges, including the need for more comprehensive training data, the incorporation of environmental data, and improvements in the estimation capabilities for various weld appearance features. This research serves as a step towards the automation of welding processes in the shipbuilding industry and provides directions for future research.

Repository Public URL： https://hdl.handle.net/2324/7337398

Event date： 2024.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ミューザ川崎シンフォニーホール＋オンライン（ハイブリッド）   Country：Japan  

Precautions of Material Selection and Consideration of Design Method for Stereolithography 3D Printer,
Sai Madokoro, Koji Gotoh,
1DCAD-MBD Symposium 2023

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 銀杏会館   Country：Japan  

Consideration on short crack propagation resistance in SM490 steels with different ΔKth.
Yoshihiro HYODO, Masao YUGA, Yasuyuki KURIHARA, Thi-Huyen Doan, Takahiro SAKIMOTO, Yoshiaki MURAKAMI, Tetsuya TAGAWA，Koji GOTOH,
Japan Welding Society Symposium 2023.

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 銀杏会館   Country：Japan  

A study of the effects of laser irradation and localized carburizing treatment on the fatigue strength improvement of welded joints,
Kazutaka TERATSUJI, Tomoya UCHIMURA and Koji GOTOH,

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 銀杏会館   Country：Japan  

Consideration on short crack propagation resistance in SM400 steels with different ΔKth,
Yoshihiro HYODO, Masao YUGA, Yasuyuki KURIHARA, Thi-Huyen Doan, Takahiro SAKIMOTO, Yoshiaki MURAKAMI, Tetsuya TAGAWA and Koji GOTOH

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 銀杏会館   Country：Japan  

A study of the effects of laser irradiation and localized carburizing treatment on the fatigue strength improvement of welded joints.
Kazutaka TERATSUJI，Tomoya UCHIMURA，Koji GOTOH,
Japan Welding Society Symposium 2023.

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：出島メッセ長崎（長崎市）   Country：Japan  

Basic Research on the Use of Structural Adhesives in Hull Construction.
Hiroyuki Onizuka, Shuichi Yamatoki, Koji Hifumi, Kazutomo Ito, Shohei Aramaki , Koji Gotoh, Koji Murakami, Toshiaki Iwata.
JASNAOE 2023 Annual Autum Meeting.
Nov.27-28, 2023.

Event date： 2023.11

Language：English   Presentation type：Oral presentation (general)  

Venue：International Conference Center Hiroshima   Country：Japan  

Other Link： https://fatigue2022.org/

Repository Public URL： https://hdl.handle.net/2324/7159845

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Pukyong National University   Country：Korea, Republic of  

In numerical simulations of fatigue crack propagation, the true stress-true strain relationship under cyclic loading should be considered, but in simulations modelling crack opening behaviour, the stress-strain relationship of the material is regarded as rigid plastic or isotropically hardened elastic-plastic material from the point of view of model simplification.
In this study, the true stress-true strain relationship under cyclic loading, estimated from the true stress-true strain relationship under monotonic tensile loading, is implemented in fatigue crack propagation simulations of work-hardened materials proposed by some of authors.
Fatigue crack growth curves under the following three loadings, (1) constant cyclic loading under different stress ratios, (2) two-stage block loading cycles, (3) constant cyclic loading with a spike load, were estimated and compared with the measured results obtained in previous studies.
The results show that the accuracy of the fatigue crack growth estimation is better than the conventional stress-strain relationship assuming elastic-perfectly plastic materials.

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Pukyong National University   Country：Korea, Republic of  

The purpose of this paper is to confirm fatigue strength of welded joints can be improved by grain refinement using laser irradiation and localized carburization considering corrosion and abrasion.
The measured temperature histories due to laser irradiation were compared with theoretical solutions for moving and instantaneous line heat sources, and it was confirmed that the temperature history could be estimated well using moving heat source. Maximum temperature and time required from 800 ℃ to 500 ℃ (Δt8/5) of the grain refinement region are obtained by applying moving heat source.

Four-point bending fatigue tests were conducted on T-joint specimens as welded, laser irradiated, and locally carburized.
As a result, number of cycles to failure of the specimens which locally carburized and laser irradiated were equivalent and they are longer than that of the specimens as-welded.
The main reason is locally carburized and laser irradiated had more gentler toe shapes than as-welded. However, the porosity was observed in the carburized specimen.
It can affect fatigue strength, further improvement of fatigue strength was expected by eliminating it.

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Pukyong National University   Country：Korea, Republic of  

Laser-arc hybrid welding (LAHW) is an advanced welding process that combines arc and laser welding as one molten pool.
Compared with conventional arc welding, LAHW can be performed higher welding speeds with narrower grooves, and weld deformation can be significantly reduced.
When LAHW is applied to construction of structural members, the welding is generally performed in a flat position because it is automatic welding system is applied from the viewpoint of safety in the work environment.
Flat position (PA), it is expected to be applied to many welds of large steel structures by applying LAHW to horizontal position.
However, the application of LAHW in the construction of large structures is expected by expanding the applicable welding position.
In this study, butt joints with a plate thickness of 20 mm were fabricated in the horizontal position (PC) as a target of welding position in LAHW.
By trial and error, referring to the welding conditions in the flat position, the welding conditions that produced a sound weld bead appearance were derived.
However, molten metal was sagging at some of lower weld bead edge of the front bead.
A sliding jig was designed to prevent the front bead sagging.
As a result, the sagging was prevented and it was expected that the jig was effective in relaxing the shape of the weld toe for improving the fatigue strength of the joint.
In the construction stages of large structures, it is difficult to maintain a constant root gap over the entire length of the weld line, so it is desirable to extend the allowable range of the initial gap. Therefore, we attempted to process with an initial root gap of 1.5 mm.
However, we were unable to find welding conditions that would avoid undercutting and melting-in, and confirmed that the applicable limit of the initial root gap is 1.0 mm for the construction method studied in this study.

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：建築会館   Country：Japan  

Effect of cutting fluid on mechanical properties of Nylon12 parts fabricated by SLS 3D printer was investigated.
There was a difference of approximately 30% in tensile strength between the "As build material immersed in cutting fluid (build direction: vertical)" and the "material with surface finishing by cutting processing (build direction: horizontal)".
This result suggest that caution should be taken in strength calculations during the design phase when using Nylon12 parts fabricated by SLS 3D printer exposed to cutting fluid environments.

Repository Public URL： https://hdl.handle.net/2324/7152003

Event date： 2023.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：建築会館   Country：Japan  

Development of Lightweight Robot Arm Components Using Generative Design,
Sai Madokoro, Koji Gotoh,
Design Symposium 2023

Repository Public URL： https://hdl.handle.net/2324/7152001

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：日本大学工学部   Country：Japan  

Development of Lightweight Parts for Industrial Robot s by Generative Design,
Sai Madokoro, Koji Gotoh,
Research Presentation Lecture for the 2023 Fall Conference, Japan Society for Design Engineering

Repository Public URL： https://hdl.handle.net/2324/7151995

Event date： 2023.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学 伊都キャンパス   Country：Japan  

Study on fabrication of butt welded joints of thick plates by laser-arc hybrid welding in horizontal position (PC);
Toshiki Tsuruoka, Tomoya Uchimura, Koji Gotoh;
Annual meeting of the Kyushu Branch of the Japan Welding Society, held on 31 August 2023.

Event date： 2023.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学 伊都キャンパス   Country：Japan  

Study on a method of one-pass construction of thick plates by laser/arc hybrid welding without the use of backing material;
Hiroo Kobayashi, Toshiki Tsuruoka, Tomoya Uchimura, Koji Gotoh;
Annual meeting of the Kyushu Branch of the Japan Welding Society, held on 31 August 2023.

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：くにびきメッセ（島根県松江市）   Country：Japan  

Study on the Application of Laser-arc Hybrid Welding with REM Additive Welding consumables in the Hull Construction Stage,
GOTOH Koji, NAKADA Tomoya, UCHIMURE Tomoya, ANDO Akiyoshi, MATSUSHITA Muneo, HANDA Tsunehisa and IGI Satoshi,
National Meeting of Japan Welding Society, September 2022.

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学 伊都キャンパス   Country：Japan  

Experimental Investigation on Stress-Strain Relationship of Steel under Cyclic Loading,
Tsukasa Shimooka, Koji Murakami, Kazuki Matsuda and Koji Gotoh,
Annual meeting of the Kyushu Branch of the Japan Welding Society held on 1 September.

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学 伊都キャンパス   Country：Japan  

A Study on Prediction of Fillet Weld Bead Shape Using Machine Learning with Welding Conditions and Welding Noise as Input Variables,
Yong-Yi Feng, Norihiro Watanabe, Kento Yamazaki, Kazuki Matsuda and Koji Gotoh,
Annual meeting of the Kyushu Branch of the Japan Welding Society held on 1 September.

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学 伊都キャンパス   Country：Japan  

Basic Study on Grain Refinement by Laser Irradiation for Fatigue Strength Improvement,
Kazuyuki Teratsuji, Tomoya Uchimura, Kazuki Matsuda and Koji Gotoh,
Annual meeting of the Kyushu Branch of the Japan Welding Society held on 1 September.

Event date： 2022.7

Language：English   Presentation type：Oral presentation (general)  

Venue：GRAND NIKKO TOKYO DAIBA   Country：Japan  

The development of an automatic weld visual inspection system applicable to weld bead visual inspection in shipyards is expected to reduce costs through man-hour reduction, improve weld quality, and shorten the repair process.
Although many studies have been conducted on the automation of weld bead visual inspection, most of them were based on image analysis.
However, in order to apply image analysis, it is necessary to remove residual slag from the bead surface after welding before taking images, which is not desirable considering the production process in shipyards.
The author's research group has been studying a method to predict weld bead appearance by deep learning using welder log data (current, voltage, and welding wire feed rate) and fixed welding conditions (torch angle, etc.) as inputs.
In this study, several improvements were made to the prediction of the leg length and undercut depth of the T-shaped joint.
These improvements significantly improved the adjusted coefficient of determination, a measure of prediction accuracy, to 0.96 for leg length prediction and 0.93 for undercut depth prediction, resulting in improved prediction accuracy for leg length and undercut depth.

Repository Public URL： https://hdl.handle.net/2324/4822552

Event date： 2022.7

Language：English   Presentation type：Oral presentation (general)  

Venue：GRAND NIKKO TOKYO DAIBA   Country：Japan  

This study is concerned with the development of a system for automatically carrying out visual inspections of the external appearance of welders in the welder's skills certification examination, without requiring extensive experience in visual inspections, and presents the results of the development of a prototype of such a system.
The developed system handles the weld bead shape measured with a 3D scanner as point data in 3D space, and matches it with the evaluation criteria for the welder qualification test, such as bead width, reinforcement of weld height and undercut depth, to enable a pass/fail decision to be made immediately after the test is taken.
In addition, the joint geometry can be stored as high-precision point cloud digital data, allowing another visual inspection to be carried out even after the specimen has been processed for bending tests after visual inspection.

Event date： 2022.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島国際会議場（広島市）・Web会議   Country：Japan  

Basic Research on Local Carburizing Treatment by Laser Irradiation for Fatigue Strength Improvement of Welded Joints,
Takehiro Tamon, Koji Gotoh, Yasuhiro Morizono
JASNAOE Anual Spring Meeting 2022 (May 26 and 27), International Conference Center Hiroshima (and On line meeting)

Event date： 2022.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島国際会議場（広島市）・Web会議   Country：Japan  

A Study on Frame Length and Frame Shift of Training Data for Automatic Inspection of Weld Bead Appearance Using Deep Learning,
Norihiro Watanabe, Kento Yamasaki, Koji Gotoh
JASNAOE Anual Spring Meeting 2022 (May 26 and 27), International Conference Center Hiroshima (and On line meeting)

Event date： 2022.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島国際会議場（広島市）・Web会議   Country：Japan  

Experimental and Analytical Study on Wear Coefficient of Mooring Chain by Using 3-D Measurement,
Takaaki Murakami, Takaaki Takeuchi, Tomoaki Utsunomiya, Koji Gotoh,
JASNAOE Anual Spring Meeting 2022 (May 26 and 27), International Conference Center Hiroshima (and On line meeting)

Event date： 2021.12