| Koji GOTOH | Last modified date：2024.04.24 |
Professor /
Structural Engineering of Ship and Marine Systems /
Department of Marine Systems Engineering /
Faculty of Engineering
Presentations
| 1. | Feng Yongyi, Gotoh Koji, Prediction of weld bead shape and defects by deep learning using welding conditions and acoustic features during welding as input variables, 3rd Hungary-Korea-Japan Joint Seminar on Design, Fabrication, and Maintenance of Welded Steel Structures, 2024, 2024.03. |
| 2. | 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. . |
| 3. | 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.. |
| 4. | 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. . |
| 5. | Yoshihiro HYODO, Masao YUGA, Yasuyuki KURIHARA, Thi-Huyen Doan, Takahiro SAKIMOTO, Yoshiaki MURAKAMI, Koji GOTOH, Tetsuya TAGAWA, Consideration on short crack propagation resistance in SM490 steels with different ΔKth., Fatigue 2022+1 (13th International Fatigue Congress), 2023.11, [URL].  |
| 6. | Precautions of Material Selection and Consideration of Design Method for Stereolithography 3D Printer, Sai Madokoro, Koji Gotoh, 1DCAD-MBD Symposium 2023. |
| 7. | 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. |
| 8. | 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, . |
| 9. | Tsukasa SHIMOOKA, Koji MURAKAMI, Kazuki MATSUDA, Koji GOTOH, Numerical simulation of fatigue crack growth with stress-strain relationship under cyclic loading, The 36th Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2023), 2023.10, 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.. |
| 10. | Toshiki TSURUOKA, Tomoya NAKADA, Tomoya UCHIMURA, Kazuki MATSUDA, Koji GOTOH, Study on fabrication of butt welded joints of thick plates by laser-arc hybrid welding in horizontal position, The 36th Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2023), 2023.10, 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.. |
| 11. | Kazutaka TERATSUJI, Tomoya UCHIMURA, Kazuki MATSUDA, Koji GOTOH, Improvement of fatigue strength of welded joints by grain refinement using laser irradiation and locally carburized, The 36th Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2023), 2023.10, 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.. |
| 12. | Sai Madokoro, Koji Gotoh, Effect of Water-soluble Cutting Fluid on Mechanical Properties of Nylon12 Manufactured by SLS 3D Printer, The Advanced Technology in Experimental Mechanics and International DIC Society Joint Conference 2023 (ATEM-iDICs '23), 2023.10, 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.. |
| 13. | Development of Lightweight Robot Arm Components Using Generative Design, Sai Madokoro, Koji Gotoh, Design Symposium 2023. |
| 14. | 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. |
| 15. | 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.. |
| 16. | 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.. |
| 17. | B L Josefson, B-Q Chen, K Gotoh, F Fang, K Liu, S van Duin, P Dong, Benchmark Study of Welding Deformations in Stiffened Plate, ASME 2022 41st International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2022), 2022.06, 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.. |
| 18. | 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.. |
| 19. | 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.. |
| 20. | 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.. |
| 21. | 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.. |
| 22. | Norihiro Watanabe, Kento Yamasaki, Koji Gotoh, A Study for Automatic Inspection of Leg Length and Undercut in the T-shaped Joint using Deep Learning, IIW 2022 International Conference on Welding and Joining, 2022.07, 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.. |
| 23. | Tomoya Uchimura, Yosuke Koba, Tomomichi Simizu, Junichi Hirata, Hiroyuki Kobayashi, Koji Gotoh, Development of a Prototype 3D Measuring and Judging System to Improve the Accuracy of Visual Inspection of Weld Bead Appearance and to Digitise Inspection Results for Welder Qualification Tests, IIW 2022 International Conference on Welding and Joining, 2022.07, 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.. |
| 24. | 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). |
| 25. | 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). |
| 26. | 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). |
| 27. | Katsuhito ITO, Koji MURAKAMI, Koji GOTOH and Tomoaki UTSUNOMIYA, Development of a Test Machine to Reproduce the Wear Behavior of Chains Mooring Offshore Wind Turbines, 34th Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2020/21), 2021.12, 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. . |
| 28. | Takehiro TAMON and Koji GOTOH, A Study on Working Conditions for Improving Fatigue Strength of Welded Joints by Localized Carburizing Treatment Using Laser Irradiation, 34th Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2020/21), 2021.12, 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.. |
| 29. | 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 The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2021 Annual Autumn Meeting.. |
| 30. | Approach to Optimistic Process of Tack Welding by Laser in Butt Joint, Takamori Uemura and Koji Gotoh The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2021 Annual Autumn Meeting.. |
| 31. | Shuichi Tsumura, Koji Gotoh, Deriving Welding Conditions of Full-Penetration Tee Joint for One-Side Single Pass Welding Fabricated with Laser-Arc Hybrid Welding, 2021 International Conference on Robust Quality Engineering (ICRQE 2021), 2021.09, Laser-arc hybrid welding is a high-quality welding technology, and it is expected to improve the productivity of manufacturing large welded structures such as ship hulls and offshore structures. Applications of this technology allow the replacement of fillet-welded joints in structures with full-penetration welded joints. This replacement should improve the fatigue performance and deformation. However, many welding conditions can become a control factor in hybrid welding due to using a laser heat source and an arc heat source at the same time, thereby making it very difficult to optimize the welding conditions using a multi-way layout. In addition, the robustness of hybrid welding is not enough to be applied to the shipbuilding. This study focused on the full-penetration tee joint for one-side single pass welding and reports the results of optimizing welding conditions using the L18 and L9 orthogonal tables. These experiments confirm even with the S/N ratio of smaller-is-better response, it is possible to derive welding conditions that are robust to the noise factors. Also, it is confirmed that the height of the laser irradiation position most affect the S/N ratio among the noise factors. In addition, the control factors related to the arc heat source were not expected to affect the bead shape of the non-welded side, but it confirmed that these control factors affect the S/N ratio of the non-welded side.. |
| 32. | Study on extending the thickness range of transverse horizontal welding in laser-arc hybrid welding, Tomoya Nakada, Tomoya Uchimura, Takamori Uemura and Koji Gotoh, Annual meeting of the Kyushu Chapter of the Japan Welding Society.. |
| 33. | 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, Annual meeting of the Kyushu Chapter of the Japan Welding Society.. |
| 34. | T. Uemura, K. Gotoh, I. Uchino, Studies on Expansion of Laser-Arc Hybrid Welding to Horizontal and Vertical-Up Welding, IIW 2021 Commission XV Design, Analysis and Fabrication of Welded Structures, 2021.07, Laser arc hybrid welding (LAHW) is an advanced welding method that combines arc welding and laser welding and can achieve deep penetration and reduction of welding deformation compared to practical arc welding. Since the equipment of LAHW is relatively large, it is common to target flat position (PA) as the welding position. On the other hand, expansion of the applicable positions enables to apply the high-quality welded joints fabricated by LAHW to many welded joints in large steel structures. In this study, as establishment of weldability in the horizontal position (PC) and the vertical-up position (PF) to expand the applicable range of LAHW in the large steel structures, the LAHW system with a robot manipulator was used. Suitable LAHW conditions to fabricate the butt welded joint with a welding length 1,000 mm for these positions were established by various investigations including the molten pool observation. At the first stage of our investigation, the authors thought that it would be easier to use the backing sheet for the fabrication of the butt joint in the vertical-up position. But it was confirmed that the toughness of the joint might decrease because of dilution of specific components contained in the backing sheet into weld metal. Therefore, it was confirmed that the fabrication was performed without using the backing sheet. After that, the quality of these joints was evaluated in accordance with the “Laser Arc Hybrid Welding Guidelines” (ClassNK) by the Nippon Kaiji Kyokai and confirmed that they meet the standards.. |
| 35. | Development of Mooring Chain Wear Behavior Reproduction Test Machine in Underwater Environment, Koji Gotoh, Koji Murakami ,Tomoaki Utsunomiya and Iku Sato, The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2021 Annual Spring Meeting.. |
| 36. | 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, The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2021 Annual Spring Meeting.. |
| 37. | 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, The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2021 Annual Spring Meeting.. |
| 38. | 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 The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2021 Annual Spring Meeting.. |
| 39. | 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 The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2021 Annual Spring Meeting.. |
| 40. | Fundamental Study on Improving Fatigue Life of Welded Joints Locally Carburized by Laser Irradiation, Takehiro TAMON, Takamori UEMURA and Koji GOTOH, Annual meeting of Japan Welding Society, Kyushu-chapter, November, 2020.. |
| 41. | 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 Annual Autumn Meeting of The Japan Society of Naval Architects and Ocean Engineers 2019, Himeji, Hyogo, Japan. |
| 42. | 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, Annual Autumn Meeting of The Japan Society of Naval Architects and Ocean Engineers 2019, Himeji, Hyogo, Japan. |
| 43. | Hisao Narimatsu, Masakazu Kuwada and Koji Gotoh, A Study on using Hot-rolled Steel Sheet for Ship Superstructure, The 14th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2019), 2019.09, 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.. |
| 44. | Koji Gotoh, Takamori Uemura, Issei Uchino, Hisao Narimatsu, Toshimitsu Maeda, Takumi Torigoe and Atsuo Moriyama., Overview of the Joint Industrial Project for Practical Application of Laser-Arc Hybrid Welding in Construction of General Merchant Ships in Japan, The 14th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2019), 2019.09, 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.. |
| 45. | Koji GOTOH, Tetsuya UEDA, Koji MURAKAMI, TOMOAKI UTSUNOMIYA, Wear Performance of Mooring Chain in Wet Environment with Substitute Ocean Water, ASME 38th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2019), 2019.06, 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.. |
| 46. | Takayuki YOTSUZUKA, Yusuke ENDO, Eiji NIINO, Koji GOTOH, A Study on Unification of Welding Consumables in Construction of Chemical Cargo Tankers Made of Duplex Stainless Steel - Evaluation of Static Strength of Welded Joint -, ASME 38th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2019), 2019.06, 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.. |
| 47. | Toshihiro FUJII, Koji GOTOH, Junichi DEGUCHI, Koji MURAKAMI, A Study on Improvement of Fatigue Performance by Shot Blasted Surface Treatment, ASME 38th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2019), 2019.06, 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.. |
| 48. | 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, Annual meeting of Japan Welding Society, Kyushu-chapter, June 20, 2019.. |
| 49. | 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, Annual meeting of Japan Welding Society, Kyushu-chapter, June 20, 2019.. |
| 50. | 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, Annual meeting of Japan Welding Society, Kyushu-chapter, June 20, 2019. |
| 51. | Fundamental Study of Automatic Inspection of Weld Bead Appearance by Machine Learning, Naoki Morihira Norihiro Watanabe and Koji Gotoh, JASNAOE Annual Spring Meeting & Conference 2019. . |
| 52. | 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 and Koji Gotoh, JASNAOE Annual Spring Meeting & Conference 2019.. |
| 53. | 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 and Atsuo Moriyama, JASNAOE Annual Spring Meeting & Conference 2019.. |
| 54. | 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 and Atsuo Moriyama, JASNAOE Annual Spring Meeting & Conference 2019.. |
| 55. | 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 and Atsuo Moriyama JASNAOE Annual Spring Meeting & Conference 2019.. |
| 56. | 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 and Atsuo Moriyama JASNAOE Annual Spring Meeting & Conference 2019.. |
| 57. | 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, 91th annual meeting of Japan Laser Processing Society (JLPS), Osaka, Japan. |
| 58. | Quantitative Wear Estimation for Mooring Chain of Floating Structures and Its Validation Takaaki Takeuchi, Tomoaki Utsunomiya, Koji Gotoh, Iku Sato, JASNAOE Annual Spring Meeting & Conference 2019.. |
| 59. | Koji GOTOH, Takamori UEMURA, Issei UCHINO, Hisao NARIMATSU and Atsuo MORIYAMA, Fundamental Studies on Application of Laser-Arc Hybrid Welding for Manufacturing Primary Structural Members in General Merchant Ships, The 8th International Congress on Laser Advanced Materials Processing (LAMP2019), The 8th International Symposium on High Power Laser Processing (HLP2019), 2019.05, 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.. |
| 60. | 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, Annual Autumn Meeting of The Japan Society of Naval Architects and Ocean Engineers 2018, Kashiwa-no-ha Conference Center, Kashiwa-shi, Chiba, Japan. |
| 61. | A Study on Improvement of Fatigue Performance by Shot Blasted Surface Treatment, Toshihiro Fujii, Koji Gotoh, Jun-ichi Deguchi and Koji Murakami, Annual Autumn Meeting of The Japan Society of Naval Architects and Ocean Engineers 2018, Kashiwa-no-ha Conference Center, Kashiwa-shi, Chiba, Japan. |
| 62. | 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, Annual Autumn Meeting of The Japan Society of Naval Architects and Ocean Engineers 2018, Kashiwa-no-ha Conference Center, Kashiwa-shi, Chiba, Japan. |
| 63. | A Study on using Hot-Coil Steel for Superstructure, Hisao Narimatsu, Masakazu Kuwada, Koji Gotoh and Yuki Sugino, Annual Autumn Meeting of The Japan Society of Naval Architects and Ocean Engineers 2018, Kashiwa-no-ha Conference Center, Kashiwa-shi, Chiba, Japan. |
| 64. | 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, Annual meeting of Japan Welding Society, Kyushu-chapter, July 7, 2018.. |
| 65. | 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, Annual meeting of Japan Welding Society, Kyushu-chapter, July 7, 2018.. |
| 66. | Koji GOTOH, Masataka NAKAGAWA, Koji MURAKAMI, TOMOAKI UTSUNOMIYA, Effect of Tensile Force for Wear Performance of Mooring Chain, ASME 37th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2018), 2018.06, 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.. |
| 67. | Investigation on Specific Wear Amount of Mooring Chain by Pin-on-disk Wear Test, Kazuki Yamane, Masataka Nakagawa, Tomoaki Utsunomiya and Koji Gotoh JASNAOE Annal Spring Meeting 2018.. |
| 68. | Study on Wear Estimation Method and Dynamic Behavior for Mooring Chain of Floating Structures, Takaaki Takeuchi, Tomoaki Utsunomiya and Koji Gotoh JASNAOE Annal Spring Meeting 2018.. |
| 69. | A Study of measurement accuracy of RPG load of the fatigue crack propagation test, Koji Murakami and Koji Gotoh, Japan Welding Society Welding Structure Symposium 2017.. |
| 70. | Extension of the stress intensity factor weight function for a surface crack and estimation of crack opening displacement based on Paris' reciprocity theorem, Yoshifumi Takaki and Koji Gotoh, Japan Welding Society Welding Structure Symposium 2017.. |
| 71. | Shape Evolution of Fatigue Surface Crack under In-plain Biaxial Cyclic Loading Yosuke, Anai, Toshio Niwa and Koji Gotoh JASNAOE Annal Autum Meeting 2017.. |
| 72. | 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 JASNAOE Annal Autum Meeting 2017.. |
| 73. | Yoshifumi TAKAKI, Koji GOTOH, Weight Function for Stress Intensity Factor of a Surface Crack with a Wide Range of Aspect Ratio on Crack Shape, 31st Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2017), 2017.09, 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. . |
| 74. | Koji MURAKAMI, Koji GOTOH, Practical Determination Method of the Threshold Stress Intensity Factor Range DKth, 31st Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2017), 2017.09, 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.. |
| 75. | Masataka NAKAGAWA, Koji GOTOH, Koji MURAKAMI, Tomoaki UTSUNOMIYA, A study on the wear performance of the mooring chain for floating wind turbine, 31st Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2017), 2017.09, 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.. |
| 76. | TAkaaki TAKEUCHI, Tomoaki UTSUNOMIYA, Kimihiro TOH, Koji GOTOH, Development of Wear Estimation Method for Mooring Chain of Floating Structures, 31st Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2017), 2017.09, 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.. |
| 77. | Ryuhei TAKESHITA, Yuki SUGINO, Naoki MORIHIRA, Koji GOTOH, Some consideration for Application of Laser-Arc Hybrid Welding in Hull Construction Stages, 31st Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2017), 2017.09, 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. . |
| 78. | A Study on the Effect of Welding Conditions on Bead Shape and Sputtering in Laser-Arc Hybrid Welding UCHINO Issei and GOTOH Koji FY2017 Autumn National Meeting of Japan Welding Society. |
| 79. | A Study on a gap tolerance for Laser/arc Hybrid Welding in hull construction stages TAKESHITA Ryuhei, SUGINO Yuki, MORIHIRA Naoki and GOTOH Koji FY2017 Autumn National Meeting of Japan Welding Society. |
| 80. | Taizo YAMAMOTO, B. LIAN, Koji GOTOH, Relationship between Temperature Property and Loading Frequency of Rotating Bending Fatigue Testing Machine of Cantilever Type, Seventh International Conference on Very High Cycle Fatigue (VHCF 7), 2017.07, 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.. |
| 81. | Koji GOTOH, Koji MURAKAMI, Masataka NAKAGAWA, TOMOAKI UTSUNOMIYA, A Study on the Wear Performance of the Mooring Chain for Floating Wind Turbine, ASME 36th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2017), 2017.06, 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.. |
| 82. | Investigation on Wear Estimation Method for Mooring Chain of Floating Structures, Takaaki Takeuchi, Kimihiro Toh, Tomoaki Utsunomiya and Koji Gotoh, 2017 Annual Spring Meeting, The Japan Society of Naval Architects and Ocean Engineers, May 23 and 24, 2017, Institute of Industrial Science, the University of Tokyo, Tokyo, Japan.. |
| 83. | 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, 2017 Annual Spring Meeting, The Japan Society of Naval Architects and Ocean Engineers, May 23 and 24, 2017, Institute of Industrial Science, the University of Tokyo, Tokyo, Japan.. |
| 84. | 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 The 86th Laser Materials Processing Conference, Okayama University, Okayama ,Japan. . |
| 85. | Preliminary Investigation on Wear Performance for Mooring Chain Applied to Floating Wind Turbine， Koji Gotoh, Koji Murakami, Masataka Nakagawa and Tomoaki Utsunomiya, JASNAOE, Annual Autumn Meeting 2016.. |
| 86. | Numerical Simulation of Fatigue Crack Propagation Considering Crack Closure over Initial Crack Surfaces under Excessive Compressive Loading， Yoshifumi Takaki and Koji Gotoh, JASNAOE, Annual Autumn Meeting 2016.. |
| 87. | 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, JASNAOE, Annual Autumn Meeting 2016.. |
| 88. | Koji GOTOH, Koji MURAKAMI, Masataka NAKAGAWA, Tomoaki UTSUNOMIYA, Experimental Study on the Wear Performance of the Mooring Chain, Advanced Maritime Engineering Conference (AMEC) 2016 of 7th Pan Asian Association of Maritime Engineering Scoeties (PAAMES), 2016.10, 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.. |
| 89. | Keishi SHIMIZU, Koji GOTOH, Yosuke ANAI, Toshio NIWA, Numerical Simulation of Fatigue Crack Propagation in an Out-of-plane Gusset Welded Joints under Biaxial Tensile Loadings with Different Phases, 30th Asia Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2016), 2016.10, 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.. |
| 90. | 後藤 浩二, 福井 努, 森山 厚夫, 津村 秀一, 沢登 寛, Overview of a joint industrial project for introducing laser - hybrid welding to the construction of general merchant ships in Japan., 13th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2016), 2016.09, The introduction and application of advanced welding methods and information technologies are important to improving the efficiency of hull construction processes and to reducing production costs. Laser-arc hybrid welding technology, which has the advantages of laser and normal arc welding, has good performance and is expected to improve productivity. The Japan Ship Technology Research Association has organized a joint industry project in collaboration with universities, classification societies and shipyards to introduce this technology to the construction of general merchant ships. This paper gives an overview of the joint research project and introduces guide-lines on laser-arc hybrid welding published by ClassNK.. |
| 91. | 森影 康, 伊木 聡, 田川 哲哉, 大井 健二, 村上 幸治, 後藤 浩二, Effect of compressive residual stress on fatigue crack propagation., 13th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2016), 2016.09, Fatigue failures have sometimes taken place in weld joints due to stress concentration and tensile residual stress at the weld toe. Therefore some treatments for delaying fatigue crack initiation and propagation are necessary for 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 improvement of the large welded structure which applied the compressive residual stress field near the weld toe, not only improvement of fatigue crack initiation life but also that of fatigue crack propagation life must be discussed. However there have been few research work which deal with the fatigue crack estimation in the compressive residual stress field so far 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. . |
| 92. | Koji GOTOH, Shuichi TSUMURA, Fatigue Strength and Angular Distortion of the Full-Penetration Tee Type Joint Fabricated by One-Side Single-Pass Laser-Arc Hybrid Welding, ASME 35th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2016), 2016.06. |
| 93. | Residual stress of full penetration tee joints fabricated by laser-arc hybrid welding， Ryuhei Takeshita, Shuichi Tsumura, Koji Murakami, Koji Gotoh and Seiichro Tsutsumi, JASNAOE, Annual Spring Meeting 2016.. |
| 94. | A Study on the Strip Yield Model for a Surface Crack， Kohei Yamashita and Koji Gotoh, JASNAOE, Annual Spring Meeting 2016.. |
| 95. | A Study on The Usefulness of Laser Tack Welding for Laser/arc Hybrid Welding, Shuichi Tsumura, Ryota Aoyagi and Koji Gotoh, 2015 annual autumn meeting of JASNAOE. |
| 96. | 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 2015 annual autumn meeting of JASNAOE. |
| 97. | Numerical Simulation of Fatigue Crack Propagation Using Elastic-plastic Finite Element Analysis and a Proposal of Fatigue Crack, Kohei Yamashita and Koji Gotoh, 2015 annual autumun meeting of JASNAOE. |
| 98. | Yasushi MORIKAGE, Satoshi IGI, Kenji OI, Yuichiro JO, Koji MURAKAMI, Koji GOTOH, Effect of Compressive Residual Stress on Fatigue Crack Propagation, 14th International Conference on Pressure Vessel Technology (ICPVT-14), 2015.09, [URL], 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 o. |
| 99. | Effect of Compressive Residual Stress on Fatigue Crack Propagation, Yasushi MORIKAGE, Satoshi IGI, Kenji OI, Yuichiro JO Koji MURAKAMI and Koji GOTOH, 2015FY autumn annual meeting of Japan Welding Society. |
| 100. | Koji GOTOH, Yumi MIZUTANI, Akinori YOSHIDA, Masato MATSUO, Engineering Leaders English Program (ELEP) for Engineering Students - Overview of Education Program in School of Engineering in Kyushu University - , 2015 JSEE Annual Conference, 2015.09, 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.. |
| 101. | Strength Evaluation of Steel Welded Joint Fabricated by Laser Arc Hybrid Welding for Shipbuilding, Shuichi TSUMURA, Toshiaki IWATA, Chikahisa MURAKAMI, Shuhei FUJIMOTO and Koji GOTOH, 2015FY autumn annual meeting of Japan Welding Society. |
| 102. | Yosuke ANAI, Toshio NIWA, Koji GOTOH, Practical Formula of the Shape Evolution of a Surface Crack Under Fatigue Loading, ASME 34th International Conference on Ocean, Offshore and Arctic Engineering, 2015.06, 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.. |
| 103. | Koji GOTOH, Practical Evaluation of the Strain Rate and Temperature Effects on Fracture Toughness of Steels, ASME 34th International Conference on Ocean, Offshore and Arctic Engineering, 2015.06, 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.. |
| 104. | 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, 2015 annual spring meeting of JASNAOE. |
| 105. | Effect of Compressive Residual Stress on Fatigue Crack Propagation, Yasushi Morikage, Satoshi Igi, Kenji Oi, Yuichiro Jo, Koji Murakami and Koji Gotoh, 2015 annual spring meeting of JASNAOE. |
| 106. | A study on Fatigue Crack Growth of a Surface Crack, Yosuke Anai, Toshio Niwa, Syota Ejima and Koji Gotoh, 2015 annual spring meeting of JASNAOE. |
| 107. | Fatigue Strength of Laser-arc Hybrid Welded T-joint under Full Penetration Welding, Shuichi Tsumura, Koji Murakami and Koji Gotoh, 2015 annual spring meeting of JASNAOE. |
| 108. | Koji GOTOH, Shuichi TSUMURA and Issei UCHINO; Overview of the joint research project for introducing laser-arc hybrid welding in Japanese shipbuilding industries, LMP symposium 2015 organized by the Japan Welding Engineering Society, February 2015.. |
| 109. | 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.. |
| 110. | Numerical Simulation of Fatigue Crack Propagation under Various Loading Condition by Using Equivalent Fatigue Stress Range Method Kazuki MATSUDA and Koji GOTOH . |
| 111. | 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 . |
| 112. | A review of fatigue strength evaluation in the superimposed stress history conditions , Naoki Osawa, Koji Gotoh and Tetsuya Nakamura, 2014 Autumn annual conference on the Japan Society of Naval Architects and Ocean Engineers, Nagasaki, Japan.. |
| 113. | A Suggestion for Checking Items on Fatigue Damage Reports, Toichi Fukasawa, Naoki Osawa, Koji Gotoh and Yoshitaka Ogawa, 2014 Autumn annual conference on the Japan Society of Naval Architects and Ocean Engineers, Nagasaki, Japan.. |
| 114. | Fatigue strength of non-load carrying type Tee welded joints with large gap , Jun-ichi Deguchi and Koji Gotoh, 2014 Autumn annual conference on the Japan Society of Naval Architects and Ocean Engineers, Nagasaki, Japan.. |
| 115. | Shuichi TSUMURA, Koji MURAKAMI, Koji GOTOH, Fatigue strength of laser arc hybrid welded T-joint under full penetration welding, 28th Asian Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM2014), 2014.10. |
| 116. | Kazuki MATSUDA, Koji MURAKAMI, Koji GOTOH, Numerical simulation of fatigue crack propagation under superimposed loading histories - Mean stress effect for fatigue crack propagation -, 28th Asian Pacific Technical Exchange and Advisory Meeting on Marine Structures (TEAM2014), 2014.10, 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.. |
| 117. | Koji GOTOH, Toshio NIWA, Yosuke ANAI, Fatigue crack growth behaviour of an out-of-plane gusset welded joints under biaxial tensile loadings with different phases, 20th European Conference on Fracture (ECF 20), 2014.07, [URL], 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.. |
| 118. | Ezzarhan Abdullah, Koji GOTOH, Effect of Gap Size on the Fatigue Performance of Non-Load-Carrying Fillet Welded Joint, 24th International Ocean and Polar Engineering Conference (ISPOE 2014), 2014.06, 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).. |
| 119. | Kohei YAMASHITA, Koji GOTOH, Numerical Simulation of Fatigue Crack Propagation and Crack Opening and Closing Model by Considering the Strain-hardening Effect of Materials, 24th International Ocean and Polar Engineering Conference (ISPOE 2014), 2014.06, 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.. |
| 120. | Shuichi YAMATOKI, Yoshitaka HAMAMOTO, Koji GOTOH, Evaluation of the Stress Magnification Factor in Angled Discontinuities of Longitudinal Stiffeners, ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2014), 2014.06, 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.. |
| 121. | Koji GOTOH, Masao TAKUNO, Koichi OKADA, Sadaharu KUSUBA, Numerical Simulation of Fatigue Crack Growth of a Welded Structural Component under Block Program Fatigue Test, ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2014), 2014.06, 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.. |
| 122. | The Strip Yield Model and Numerical Simulation of Fatigue Crack Growth of Surface Crack , Kohei Yamashita, Shota Ejima and Koji Gotoh, 2014 Spring annual conference on the Japan Society of Naval Architects and Ocean Engineers, Sendai, Japan.. |
| 123. | 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, 2014 Spring annual conference on the Japan Society of Naval Architects and Ocean Engineers, Sendai, Japan.. |
| 124. | 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, 2014 Spring annual conference on the Japan Society of Naval Architects and Ocean Engineers, Sendai, Japan.. |
| 125. | Fatigue crack growth behaviour of welded built-up structures under block program fatigue test, Masao Takuno, Koichi Okada, Sadaharu Kusuba and Koji Gotoh, 2013 Autumn annual conference on the Japan Society of Naval Architects and Ocean Engineers, Osaka, Japan.. |
| 126. | Ezzarhan Abdullah, 後藤 浩二, Numerical Study of Fatigue Performance of Butt Welded Joint with U and V-notch Undercut , 日本船舶海洋工学会2013年秋季講演会, 2013.11. |
| 127. | Numerical simulation of fatigue crack propagation and crack opening and closing model considering the strain hardening effect of materials , Kohei Yamashita and Koji Gotoh, 2013 Autumn annual conference on the Japan Society of Naval Architects and Ocean Engineers, Osaka, Japan.. |
| 128. | Koji GOTOH, Kazuhiro AOYAMA, Comparison of Hull Construction Quality Standards, 12th International Symposium of Practical Design of Ships and Other Floating Structures (PRADS 2013), 2013.10, Hull construction deviations are controlled according to the shipbuilding standards which are established by each societies or the international association of classification societies (IACS) to maintain the structural integrity of hull constructions. However, most of these quality standards are not revised even though the hull structural design, the welding techniques and materials, the hull materials have been developing. Then, the improvement of hull construction quality standards is expected by considering the development of shipbuilding technologies. Comparison of nine hull construction quality standards is conducted in this report. Although these comparisons cannot find out significant difference among the standards, some characteristics and the historical background of each standard are confirmed and recommended revised parts of the quality standards are confirmed.. |
| 129. | Shuichi YAMATOKI, Seitaro ARIMATSU, Koji GOTOH, Misalignment Effect on a Three-Dimensional Cruciform Welded Joint, ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2013), 2013.06, 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 minimized. 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. . |
| 130. | Koji GOTOH, Toshio NIWA, Yosuke ANAI, Tetsuya OMORI, Yoshihisa TANAKA, Koji MURAKAMI, Fatigue Crack Propagation under Biaxial Tensile Loading, - Effect of the Phase Difference on Biaxial Loading -, ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2013), 2013.06, 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.. |
| 131. | Kazuki MATSUDA, Koji GOTOH, Numerical Simulation of Fatigue Crack Propagation under Simulated Whipping Loading Arising in Hull Structures, ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2013), 2013.06, 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.. |
| 132. | Ezzarhan Abdullah, 後藤 浩二, Practical Formula of Stress Concentration Factor for Butt Welded Joint with Undercut, 日本船舶海洋工学会2013年春季講演会, 2013.05. |
| 133. | Static Strength Evaluation of the Side-fillet Welded Joint by FE Analysis, Shuichi TSUMURA and Koji GOTOH, 2013 Spring annual conference on the Japan Society of Naval Architects and Ocean Engineers, Hiroshima, Japan.. |
| 134. | 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, 2013 Spring annual conference on the Japan Society of Naval Architects and Ocean Engineers, Hiroshima, Japan.. |
| 135. | Effect of the Geometry on Stress Variation in a Knuckle Model, Shuichi YAMATOKI and Koji GOTOH, 2013 Spring annual conference on the Japan Society of Naval Architects and Ocean Engineers, Hiroshima, Japan.. |
| 136. | Improvement of estimation procedure of the stress-strain relation under arbitrary strain rate and temperature conditions, Koji GOTOH and Naoki AKAHOSHI Annual Autumn Conference of JASNAOE 2012.. |
| 137. | Estimation of Stress Increase Ratio Caused by Misalignment, Syuich YAMATOKI, Seitaro ARIMATSU and Koji GOTOH, Annual Autumn Conference of JASNAOE 2012.. |
| 138. | Effect of Loading Mode and Thickness of an Intercalated Plate on Strength Degradation Caused by Misalignment (3rd report), Syuich YAMATOKI, Seitaro ARIMATSU and Koji GOTOH, Annual Autumn Conference of JASNAOE 2012.. |
| 139. | A Study of Determination procedure of the fatigue crack growth threshold ΔKth, Koji MURAKAMI and Koji GOTOH, Annual Autumn Conference of JASNAOE 2012.. |
| 140. | 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, Annual Autumn Conference of JASNAOE 2012.. |
| 141. | 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, Annual Autumn Conference of JASNAOE 2012.. |
| 142. | Numerical simulation of fatigue crack propagation considering the strain hardening effect of materials, Kohei Yamashita, Student Member Kazuki Matsuda and Koji Gotoh. Annual Autumn Conference of JASNAOE 2012.. |
| 143. | Numerical simulation of fatigue crack propagation considering the strain hardening effect of materials, Kohei YAMASHITA, Kazuki MATSUDA and Koji GOTOH, Annual Autumn Conference of JASNAOE 2012.. |
| 144. | Numerical Simulation of Fatigue Crack Propagation Under Superimposed Variable Amplitude Loading. Koji GOTOH and Kazuki MATSUDA Annual meeting of spring season, The Japan Society of Naval Architects and Ocean Engineers, 18th May, 2012.. |
| 145. | Practical point load weight function for stress intensity factor of a surface and an embedded crack. Koji GOTOH and Tetsuya OTAGURO Annual meeting of spring season, The Japan Society of Naval Architects and Ocean Engineers, 18th May, 2012.. |
| 146. | 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 Annual meeting of spring season, The Japan Society of Naval Architects and Ocean Engineers, 18th May, 2012.. |
| 147. | Numerical Simulation of Fatigue Life for Cruciform Joint Applied to Stainless Chemical Tankers, Hideyuki UCHIMURA, Masao TAKUNO and Koji GOTOH, Welding Structure Symposium 2001 by The Japan Welding Society, November 2011.. |
| 148. | Analysis on softening behavior under macroscopically-elastic cyclic loading condition, Seiichiro TSUTSUMI, Naoyuki YAMATO, Koji GOTOH and Fionn DUNNE, Welding Structure Symposium 2001 by The Japan Welding Society, November 2011.. |
| 149. | 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, Annual meeting of fall season, The Japan Society of Naval Architects and Ocean Engineers, 1st November, 2011.. |
| 150. | 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, Annual meeting of fall season, The Japan Society of Naval Architects and Ocean Engineers, 1st November, 2011.. |
| 151. | Fatigue Strength of Load-Carrying Type Cruciform Joint of Stainless Chemical tankers. Hideyuki UCHIMURA, Isshin FUJII and Koji GOTOH, Annual meeting of fall season, The Japan Society of Naval Architects and Ocean Engineers, 1st November, 2011.. |
| 152. | 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, International Conference on Advanced Technology in Experimental Mechanics 2011 (ATEM'11), September 19-21, 2011, Kobe International Conference Center, Kobe, Japan. |
| 153. | Fundamental study of the length of Electric Fusion socket type joint applied to the city gas pipeline Daichi MIYAMOTO and Koji GOTOH. |
| 154. | 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. |
| 155. | 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, 2011 Annual spring meeting of the Japan Society of Naval Architects and Ocean Engineers, May 19 -20, 2011. . |
| 156. | 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, Vol.11, November 2010. |
| 157. | 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, Vol.11, November 2010. |
| 158. | 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, Vol.11, November 2010. |
| 159. | 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, Vol.11, November 2010. |
| 160. | 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, Vol.11, November 2010. |
| 161. | 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). |
| 162. | 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. |
| 163. | Analyses of the Fatigue Crack Growth and the Resultant Brittle Crack Initiation from Embedded Flaws in Butt Welded Joints of Extremely Thick Plates, Koji GOTOH, Masahiro TOYOSADA, Yoichi SUMI, O Kitamura, Toshiyuki MATSUMOTO and Masanobu TOYODA Annual conference on the Japan Society of Naval Architects and Ocean Enigneering. |
| 164. | Crystal Plasticity EF Analysis on Initiation of Plastic Strain under Macroscopycally Elastic Stress State, Seiichiro TSUTSUMI, Naoyuki YAMATO, Koji GOTOH and Fionn Dunne Annual conference on the Japan Society of Naval Architects and Ocean Enigneering, West Chapter. |
| 165. | Estimation of Shape Evolution of an Embedded Elliptical Fatigue Crack, Keisuke HARADA, Koji GOTOH and Masahiro TOYOSADA, Annual conference on the Japan Society of Naval Architects and Ocean Enigneering, West Chapter. |
| 166. | 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. |
| 167. | 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 . |
| 168. | 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. |
| 169. | Calculation Method of Crack Opening Displacement by using Strip Yield Model for an embedded Elliptical Crack Yukinobu NAGATA and Koji GOTOH Annual conference of the Japan Society of Naval Architects and Ocean Engineering. |
| 170. | Numerical Simulation of Fatigue Crack Propagation Considering Work Hardening Effect Koji GOTOH, Yukinobu NAGATA, Keisuke HARADA and Koji KADOWAKI Annual conference of the Japan Society of Naval Architects and Ocean Engineering. |
| 171. | Characteristics of Crack Propagation in Aluminumu Alloy A5083-0 and A5083-H32 Series Koji GOTOH, Koji MURAKAMI, Yasuo NODA, Keiji AKIZUKI and Tutomu TAKIMOTO Annual conference of the Japan Society of Naval Architects and Ocean Engineering. |
| 172. | Applicability Evaluationof Strip Yield Model for Three Dimensional Crack Problem, Yukinobu NAGATA, Kunishige FUKUDOME and Koji GOTOH Annual conference of the Japan Society of Naval Architects and Ocean Engineering, West Japan chapter. |
| 173. | 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). |
| 174. | Stress Intensity FActor for Three Dimensional Cracks by Applying Slice Synthesis Methodology Yukinobu NAGATA and Koji GOTOH Annual Conference on the Japan Society of Naval Architects and Ocean Engineering (JASNAOE). |
| 175. | Fundamental investigation of the extended strip yield model for notched materials Koji GOTOH and Shinnosuke TSUTSUMI Annual Conference on the Japan Society of Naval Architects and Ocean Engineering (JASNAOE). |
| 176. | A practical estimation of welding deformation in the assembly stage of hull panel structures Koji GOTOH, Ryohei KAWASHIMA and Masahiro TOYOSADA International Conference of Computational and Experimental Engineering and Sciences 2008 (ICCES'08). |
| 177. | A practical estimation of welding deformation in the assemble stage of hull panel structures, Koji GOTOH, Ryohei KAWASHIMA and Masahiro TOYOSADA . |
| 178. | Estimation of shape development of a surface fatigue crack Koji GOTOH, Yukinobu NAGATA and Masahiro TOYOSADA Annual Conference of The Japan Society of Naval Architects and Ocean Engineering，May 2007. |
| 179. | Fatigue life estimation for a long fatigue crack in large-scale specimen in initiation of hull skin plate Koji GOTOH, Yukinobu NAGATA and Masahiro TOYOSADA Annual Conference of The Japan Society of Naval Architects and Ocean Engineering，November 2006. |
| 180. | A Conventional growth estimation method of multiple surface cracks generated by fatigue in the concentration region Yosuke ANAI, Koji MURAKAMI, Koji GOTOH and Masahiro TOYOSADA Annual Conference of The Japan Society of Naval Architects and Ocean Engineering，November 2006. |
| 181. | Minchoel CHO, Koji GOTOH, Masahiro Toyosada, Plastic Constraint Factor for Compact Tension Specimens, The 20th Asian Technical Exchange and Advisory Meeting on Marine Structures (TEAM 2006), 2006.10, The strip yield model is a representative cohesive force model. Primitive strip yield model was applied to an infinitely wide plate with a crack or a centre cracked plate subjected to uniform remote tensile stress (CCT specimen). The strip yield model is extended for the plates with a through thickness crack subjected to arbitrary stress distributions. The plastic constraint factor is introduced to the strip yield model in order to ensure consistency with actual crack opening behaviours. Therefore, an appropriate value of plastic constraint factor must be obtained if the strip yield model is applied to evaluate crack opening behaviours. In this paper, the plastic constraint factor for compact tension (CT) specimen is investigated by comparing the crack opening profiles obtained by extended strip yield model with elastic-plastic finite element analyses. It makes clear that the extended strip yield model with an appropriate plastic constraint factor enables to be a good agreement with FE analyses. Plastic constraint factors for CT specimen are about twice of the factors for CCT specimen. It is considered that such a difference is derived from the difference of multi-axial stress state ahead of a crack tip between CT and CCT specimens.. |
| 182. | Fatigue Crack Initiation and Propagation Analysis in the Hull Double Bottom Structural Model with a Corner Bracket by FLARP Koji GOTOH, Akira SUEDA and Masahiro TOYOSADA Mechanical Engineering Congress 2006 Japan (MECJ-06), September 2006. |
| 183. | A Simple Estimation Method of The Stress Distribution Normal to Cross Section at Weld Toe in the Non-load Carrying Joints Koji GOTOH, Yukinobu NAGATA and Masahiro TOYOSADA Mechanical Engineering Congress 2006 Japan (MECJ-06), September 2006. |
| 184. | Physical Meaning of Fictitious COD at Notch Root Masahiro TOYOSADA, Keitaro KONUMA, Pengcheng TIAN and Koji GOTOH Mechanical Engineering Congress 2006 Japan (MECJ-06), September 2006. |
| 185. | Concepts of Equivalent Distributed Stress and Representative Surface Crack in FLARP Masahiro TOYOSADA and Koji GOTOH Mechanical Engineering Congress 2006 Japan (MECJ-06), September 2006. |
| 186. | Fatigue Crack Growth in the First Grain Boundary Adjacent Notch Root Daisuke SUGITANI, Koji MURAKAMI, Koji GOTOH and Masahiro TOYOSADA Mechanical Engineering Congress 2006 Japan (MECJ-06), September 2006. |
| 187. | 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, Annual meeting of Japan Society for Engineering Education, 2006 . |
| 188. | Fatigue Damage at the Root of the Gatelip of the Water Gate Under Variable Water Pressure Due to Tide And Ocean Wave. |
| 189. | A Simple Estimation Method of the Stress Distribution Normal to Cross Section at Weld Toe in non-load carrying welded joints. |
| 190. | Mechanical Fatigue Simulation by Unconventional Plasticity Model. |
| 191. | Fatigue life assessment for structural element with bracket by numerical fatigue crack growth simulation. |
| 192. | A Comparative Study of Computational Models for Fatigue Crack Propagation. |
| 193. | FE Analysis on Mechanical Fatigue. |
| 194. | Numerical Simulation of Fatigue Crack Growth for the In-plane Gusset Welded Joint. |
| 195. | Grwoth Prediction of multiple fatigue surface cracks initiating from stress concentration region without initial defects. |
| 196. | Fatigue crack growth prediction on in-plane gusset joint. |
| 197. | Physical Meaning of the Fictitious Crack Opening Displaecement in Dugdale Model. |
| 198. | Stable Softening of Pressure Sensitive and Non-Associated Plastic Flow Materials. |
| 199. | A fatigue life prolonging method for welded built-up steel structures by the grain fining around weld toe. |
| 200. | A study of the inelastic deformation under principal stress axes rotation -Effect of the non-acoaxiality induced by anisotropy and tangential plasticity-, Seichiro TSUTSUMI, Masahiro TOYOSADA, Koji GOTOH and Koichi HASHIGUCHI, Annual meeting of Japan Welding Society, Kyushu-chapter. |
| 201. | 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, Annual meeting of Japan Welding Society, Kyushu-chapter. |
| 202. | Fatigue Life Estimation for In-plane Gusset Joint -An Application of the Fatigue Crack Growth Estimation Code ``FLARP''-. |
| 203. | A Proposal of Constitutive Equation Consdering the Effect of Strain Rate and Temperature. |
| 204. | Improvement of Constitutive Equation in Steels Considering the Effect of Strain Rate and Temperature. |
| 205. | Pysical meaning of the fictitious crack in Dugdale Model. |
| 206. | Damage Analysis of a Fish Preserve Made of Aluminum Alloy. |
| 207. | Development of Evaluation Parameter for Fracture Toughness Based on Statistical Mechanics. |
| 208. | An Practical Estimation Method of the Skin Plate Distorsion Derived from Fillet Weld. |
| 209. | A Study of Crack Depth Effect and Scattering of Fracture Toughness in Three Point Bend COD Specimen. |
| 210. | A Study on Deformation due to Thermal Cutting. |
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