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

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

Language：Japanese   Publishing type：Research paper (other academic)   Publisher：JAPAN WELDING SOCIETY  

自動車シャシー部材の耐食性向上にあたり，亜鉛めっき鋼板の適用が有効である．他方で，シャシー部材の組立ではガスシールドアーク溶接による重ねすみ肉溶接継手が多く，ルート部近傍で亜鉛蒸気の気泡が発生し易い．この気泡が溶接金属内部で気孔となり，溶接継手の機械的特性の劣化を招く．そこで本報では，気孔の低減に有効な溶接プロセスを検証した結果について報告する．

DOI： 10.14920/jwstaikai.2024s.0_4

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

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

DOI： 10.1080/09507116.2023.2282231

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CiNii Research

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN WELDING SOCIETY  

DOI： 10.2207/jjws.93.300

CiNii Research

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Language：English  

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.

CiNii Research

Language：English  

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.

CiNii Research

Language：English  

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. / Comparing measured temperature history of laser irradiation with theoretical solutions of moving heat source and instantaneous line heat source, and effective temperature range of grain refinement are investigated. Only moving heat source agreed with the measured values. Maximum temperature and time required from 800 ℃ to 500 ℃ (Δt8/5) of the grain refinement region are obtained by applying moving heat source. It is reasonable based on the theory of phase transformation. / 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.

CiNii Research

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

Advanced high strength steel sheet (AHSS) is widely used in the automotive body for weight reduction and the improvement of crash performance. For example, TS1500 MPa class hot stamped steel (1500HS steel) sheet is applied to many vehicle models. However, there is a concern that performance of spot welded joints will decline as steel strength increases. In order to further expand the application of AHSS, it is very important to have knowledge about the characteristics of spot welded joints. In this report, we investigated the tensile shear strength (TSS) of the 1500HS steel sheet. Then, we compared the joint strength and failure position of the same kind material joints and the dissimilar material joints with the 1500HS steel sheet in case of the plug failure. As a result, it was found that TSS of dissimilar material joints depend on base metal strength on lower strength steel side. However, fracture occurred on the 1500HS steel side except for joints with large difference of base metal strength. The mechanism is thought that the effect of strain concentration at the edge of nugget on the 1500HS steel side due to the increase of rotational deformation around the nugget.

DOI： 10.1080/09507116.2023.2202949

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

A method for improving the fatigue strength of thin steel sheet gas metal arc (GMA)-welded joints using weaving welding was evaluated. Weaving created peaks and valleys at the weld toe. The valley has high stress triaxiality, and plastic deformation is unlikely to occur. Fatigue cracks occurred from the peaks with gentle toe shapes. Therefore, it is considered that the fatigue strength is improved by reducing the initiation points of the crack and stress concentration at the toe. The fatigue test results showed that the fatigue limit of the weaving welding joint was improved compared with that of the normal welding joint. Furthermore, the optimal weaving condition, which is the relationship between the weaving wavelength and torch swing amplitude, was evaluated. As a consequence, when the wave density is small, the crack initiation point is not restricted to the peak. On the other hand, when the wave density is large, the peak and valley shapes merge and the weaving effect disappears. In addition, undercuts occurred when the swing amplitude became too large. The mechanism of improving the fatigue strength was considered by observing the initiation point of the fatigue microcracks.

DOI： 10.1007/s40194-023-01480-z

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN WELDING SOCIETY  

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

DOI： 10.2207/qjjws.41.217

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

This study investigates the dominant factors of fatigue strength at the root of thin-sheet lap fillet arc welds, which are frequently used in automobile chassis components. A method to improve the root fatigue strength was investigated. The direction of fatigue crack propagation at the root coincided with the direction of maximum circumferential stress range. The circumferential stress was reduced by increasing the distance from the toe to the root (penetration width). Fatigue strength originating from the root was improved in welded joints where the penetration width was increased by adjusting the welding aim point and heat input.

DOI： 10.1016/j.tafmec.2022.103667

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Yosetsu Gakkai Ronbunshu/Quarterly Journal of the Japan Welding Society  

Advanced high strength steel sheet (AHSS) is widely used in the automotive body for weight reduction and the improvement of crash performance. In general, weldability and formability of steel sheet tends to decline as steel strength increases. Hot stamping is a technique that achieves both formability and strength of steel sheet, and TS1500MPa class hot stamped steel sheet is applied to many vehicle models. On the other hand, since the joint strength characteristics of the spot weld are dominated by the melt-solidified zone and weld heat affected zone, there is a concern that performance of spot welded joints will decline as steel strength increases. In other words, in order to further expand the application of AHSS, it is very important to have knowledge about the characteristics of spot welded joints. In this report, we investigated the TSS of the TS1500MPa class hot stamped steel sheet, focusing on the characteristics of tensile shear joints. Then, we compared the joint strength and failure position of the same kind material joints and the dissimilar material joints with the TS1500MPa class hot stamped steel sheet in case of the plug failure. As a result, it was found that TSS of dissimilar material joints depend on base metal strength on lower strength steel side. However, fracture occurred on the TS1500MPa class hot stamped steel side except for joints with large difference of base metal strength. The mechanism is thought that the effect of strain concentration at the edge of nugget on the TS1500MPa class hot stamped steel side due to the increase of rotational deformation around the nugget.

DOI： 10.2207/qjjws.40.216

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Language：Japanese  

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Language：Japanese  

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Language：Japanese   Publisher：溶接学会九州支部  

CiNii Research

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：溶接学会九州支部  

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

Weld residual stress of the lap fillet GMA welding joints which was performed using two strength grades of steel sheets and two strength grades of welding wires were measured. In addition, to consider the effects of steel sheet strength and weld metal strength on welding residual stress, thermal elastoplastic analysis using FEM was carried out for the experiments. As a result of the analysis using the temperature history of the heat-affected zone as a fitting parameter, the residual stress distributions near the toe were in agreement with the measurement in the FE analysis. Comparing the residual stress distributions in the direction perpendicular to the weld line on the weld metal surface near the toe, which is the occurring point of fatigue cracks in the FE analysis results, with the same steel sheet, the higher the weld metal strength the smaller the tensile residual stress. And comparing with the same wire, the higher the steel sheet strength the higher the tensile residual stress. The reason for the former is that when using high-strength wire, cooling transformation occurs at a lower temperature than using low-strength wire. As a result, it is considered that the tensile residual stress was effectively reduced by causing transformation expansion while the surrounding strength was high. The reason for the latter is considered to be that each stress value changes based on the yield stress of the steel sheet and weld metal because the plastic strain continues to occur in each direction until transformation occurs after welding. It was considered that the larger the ratio of the hardness of the weld metal to the base metal, the smaller the ratio of the residual stress of the weld metal near the toe to the yield stress.

DOI： 10.1080/09507116.2022.2030536

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

The effect of galvannealed (GA) coating on the corona bond strengths of resistance spot welding joints was investigated. A cross tensile test was performed with removal of the nugget, using GA steel sheets and steel sheets whose coating had been removed via pickling. The maximum load with coating was lower than that without coating. When the nugget diameter was small (3√t, t: sheet thickness), GA coating reduced the corona bond strength (MPa). In contrast, when the nugget diameter was large (5√t), GA coating did not change the corona bond strength but reduced the corona bond area.

DOI： 10.1080/13621718.2021.2023964

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

Weld residual stress of the lap fillet GMA welding joints which was performed using two strength grades of steel sheets and two strength grades of welding wires were measured. In addition, in order to consider the effects of steel sheet strength and weld metal strength on welding residual stress, thermal elastoplastic analysis using FEM was carried out for the experiments. As a result of analysis using the temperature history of the heat-affected zone as a fitting parameter, the residual stress distributions near the toe were in agreement with the measurement in the FE analysis. Comparing the residual stress distributions in the direction perpendicular to the weld line on the weld metal surface near the toe, which is the occurring point of fatigue cracks in the FE analysis results, with the same steel sheet, the higher the weld metal strength the smaller the tensile residual stress. And comparing with the same wire, the higher the steel sheet strength the higher the tensile residual stress. The reason for the former is that when using high-strength wire, cooling transformation occurs at a lower temperature than using low-strength wire. As a results, it is considered that the tensile residual stress was effectively reduced by causing transformation expansion due to while the surrounding strength was high. The reason for the latter is considered to be that the each stress value changes based on the yield stress of the steel sheet and weld metal because the plastic strain continues to occur in each direction until transformation occurs after welding. It was considered that the larger the ratio of the hardness of the weld metal to the base metal, the smaller the ratio of the residual stress of the weld metal near the toe to the yield stress.

DOI： https://doi.org/10.2207/qjjws.39.218

Other Link： https://doi.org/10.2207/qjjws.39.218

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

DOI： https://doi.org/10.14920/jwstaikai.2021f.0_230

Other Link： https://doi.org/10.14920/jwstaikai.2021f.0_230

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

DOI： https://doi.org/10.1016/j.ijfatigue.2020.106087

Other Link： https://doi.org/10.1016/j.ijfatigue.2020.106087

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

DOI： https://doi.org/10.14920/jwstaikai.2020f.0_164

Other Link： https://doi.org/10.14920/jwstaikai.2020f.0_164

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

Fatigue tests were performed on GMA welded joints using a prototype steel sheets with varying amounts of C. In addition, the origin of the fatigue cracks in the thin steel GMA welded joints were investigated through observation the micro cracks in the specimens that were judged to be not fractured by fatigue limit stress in the fatigue test. As a result of plane bending fatigue test of bead-on-plate welding sheet, fatigue limit of the welded specimen did not differ much between the steel sheets. Observing the specimens which were not fractured at the fatigue limit, micro cracks often occurred at the bottom of the ripples on the weld metal surface and in the ferrite structure. It was founded that fatigue cracks in thin steel sheet GMA welding using mixed gas occurred parallel along the bottom of the ripples and parallel cracks merged with the crack growth, resulting in a zigzag propagation path on the weld joint surface. The effect of ripple on the fatigue limit was predicted by comparing estimating the fatigue limit without considering the ripple with the fatigue limit obtained from experiment. Finally, the effect of ripple on the fatigue limit was more than 10% and less than 20%. And it was implied that higher the strength of the material, the greater the effect of ripple on the fatigue limit.

DOI： https://doi.org/10.2207/qjjws.38.157

Other Link： https://doi.org/10.2207/qjjws.38.157

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

DOI： https://doi.org/10.14920/jwstaikai.2019f.0_226

Other Link： https://doi.org/10.14920/jwstaikai.2019f.0_226

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

DOI： https://doi.org/10.1080/13621718.2019.1613010

Other Link： https://doi.org/10.1080/13621718.2019.1613010

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

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

DOI： https://doi.org/10.14920/jwstaikai.2018f.0_240

Other Link： https://doi.org/10.14920/jwstaikai.2018f.0_240

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

DOI： https://doi.org/10.14920/jwstaikai.2017f.0_18

Other Link： https://doi.org/10.14920/jwstaikai.2017f.0_18

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

DOI： https://doi.org/10.14920/jwstaikai.2016f.0_368

Other Link： https://doi.org/10.14920/jwstaikai.2016f.0_368

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

DOI： https://doi.org/10.14856/conf.20.0_489

Other Link： https://doi.org/10.14856/conf.20.0_489

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

DOI： https://doi.org/10.1016/j.marstruc.2014.12.005

Other Link： https://doi.org/10.1016/j.marstruc.2014.12.005

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

Fatigue crack propagation behavior under superimposed loading histories with several mean stress conditions 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 for fatigue crack propagation. The parameter, which is based on the plastic hysteresis consuming in the vicinity of a crack tip,is applied to extract the effective loading for fatigue crack propagation and implemented into the numerical simulation code of fatigue crack propagation. Fatigue crack propagation tests under various superimposed loading conditions, which contain several constants and variable mean stress, are performed and comparison of fatigue crack propagation histories 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 superimposed loading histories with different frequencies. Subsequently, practical fatigue strength evaluation based on the linear cumulative fatigue damage parameter were conducted to investigate the tendency of fatigue damage value affected by mean stresses.

DOI： https://doi.org/10.2534/jjasnaoe.20.119

Other Link： https://doi.org/10.2534/jjasnaoe.20.119

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

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

DOI： https://doi.org/10.2534/jjasnaoe.17.75

Other Link： https://doi.org/10.2534/jjasnaoe.17.75

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

Numerical Simulation of Fatigue Crack Propagation Under Simulated Whipping Loading Arising in Hull Structures, Kazuki Matsuda, Koji Gotoh, OMAE2013-10985, V003T03A037; 7 pages.

DOI： https://doi.org/10.1115/OMAE2013-10985

Other Link： https://doi.org/10.1115/OMAE2013-10985

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

Numerical simulation of fatigue crack propagation under superposed loading histories with two different frequencies, Koji GOTOH，Kazuki MATSUDA，O KITAMURA, Proc. HYDROELASTICITY 2012, pp 287～297

Event date： 2024.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Kure, Hiroshima   Country：Japan  

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

Event date： 2024.4

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Osaka University   Country：Japan  

DOI： https://doi.org/10.14920/jwstaikai.2024s.0_4

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Country：Korea, Republic of  

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

Event date： 2023.10

Language：English  

Venue：Busan   Country：Korea, Republic of  

The purpose of this paper is to confirm fatigue strength of welded joints can be improved by grain refinement using laser irradiation and localized carburization considering corrosion and abrasion. Comparing measured temperature history of laser irradiation with theoretical solutions of moving heat source and instantaneous line heat source, and effective temperature range of grain refinement are investigated. Only moving heat source agreed with the measured values. Maximum temperature and time required from 800 ℃ to 500 ℃ (Δt8/5) of the grain refinement region are obtained by applying moving heat source. It is reasonable based on the theory of phase transformation. 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.

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Event date： 2023.10

Language：English  

Venue：Busan   Country：Korea, Republic of  

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

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Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan   Country：Korea, Republic of  

In numerical simulations of fatigue crack propagation, the true stress-true strain relationship under cyclic loading should be considered, but in simulations modelling crack opening behaviour, the stress-strain relationship of the material is regarded as rigid plastic or isotropically hardened elastic-plastic material from the point of view of model simplification. In this study, the true stress-true strain relationship under cyclic loading, estimated from the true stress-true strain relationship under monotonic tensile loading, is implemented in fatigue crack propagation simulations of workhardened 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 stressstrain relationship assuming elastic-perfectly plastic materials.

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Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡県   Country：Japan  

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

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡県   Country：Japan  

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

Event date： 2022.9

Language：Japanese  

Venue：福岡県   Country：Japan  

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Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡県   Country：Japan  

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Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡県   Country：Japan  

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Event date： 2022.7

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Kazuki Matsuda, Yoshinari Ishida, Shinji Kodama, Fatigue strength improvement method for thin sheet GMA welding joints by weaving, International Institute of Welding, XII-2494-2022, Tokyo, July 20-21, 2022

Event date： 2022.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Kazuki Matsuda, Yoshinari Ishida, Shinji Kodama, Fatigue strength improvement method for thin sheet GMA welding joints by weaving, International Institute of Welding, XII-2494-2022, Tokyo, July 20-21, 2022

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Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：WEB開催   Country：Japan  

Other Link： https://doi.org/10.14920/jwstaikai.2021f.0_230

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：WEB開催   Country：Japan  

Other Link： https://doi.org/10.14920/jwstaikai.2021f.0_188

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：WEB開催   Country：Japan  

Other Link： https://doi.org/10.14920/jwstaikai.2020f.0_164

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Other Link： https://doi.org/10.14920/jwstaikai.2019f.0_226

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.9

Language：Japanese  

Venue：愛媛県   Country：Japan  

Other Link： https://doi.org/10.14920/jwstaikai.2018f.0_240

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡県   Country：Japan  

Other Link： https://doi.org/10.14920/jwstaikai.2017f.0_18

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：群馬県   Country：Japan  

Other Link： https://doi.org/10.14920/jwstaikai.2016f.0_368

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：群馬県   Country：Japan  

Other Link： https://doi.org/10.14920/jwstaikai.2016f.0_378

Event date： 2015.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Other Link： https://doi.org/10.14856/conf.20.0_489

Event date： 2014.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Event date： 2014.10

Language：English   Presentation type：Oral presentation (general)  

Country：Turkey  

Event date： 2014.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宮城   Country：Japan  

Event date： 2013.7

Language：English   Presentation type：Oral presentation (general)  

Country：France  

Event date： 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan  

Event date： 2012.11

Language：Japanese  

Venue：千葉   Country：Japan  

Event date： 2012.9

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2012.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島   Country：Japan  

Event date： 2012.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：兵庫県   Country：Japan  

Event date： 2011.9

Language：English   Presentation type：Oral presentation (general)  

Country：Korea, Republic of  

Event date： 2011.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：4

Proceedings of International Conference Number of peer-reviewed papers：1