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Hirohata Mikihito,Itoh Yoshito 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.1
In order to propose a simplified simulation method using finite element (FE) model for predicting deformation and residual stress generated by multi-pass butt welding, a series of experiments and numerical analyses were carried out. 3-pass butt welding of steel plates was simulated by the thermal elasto-plastic analysis with shell elements and with solid elements respectively. A heat input model for considering the temperature distribution in the thickness direction in shell elements was proposed. The validity of the heat input model was verified by comparing analytical results with experimental results or other analytical results using solid elements. Furthermore, the effectiveness for saving computing time by using shell elements was confirmed from the comparison with the case using solid elements. It was confirmed that the welding out-of-plane deformation and residual stress could be predicted with high accuracy by the proposed method. The computing time was around 14% of that by the precise model with solid elements.
Effect of Heating Correction on Compressive Behavior of Projection Panels
Mikihito Hirohata,You-Chul Kim 한국강구조학회 2007 International Journal of Steel Structures Vol.7 No.2
A series of compresive tests for cruciform column projection panels was carried out so as to elucidate the effect of heatingcorection on compressive behavior of projection panels. Based on the experimental results, buckling strengths of the projectionpanels corected by heating became lower than those of the virgin panels because of residual imperfection, which was theheating were almost same as those of the virgin panels. The buckling modes of the panels corected by heating changedvariously comparing with those of the virgin panels due to both residual imperfection and increase of yield stres by workhardening.
Mikihito Hirohata,You-Chul Kim 한국강구조학회 2008 International Journal of Steel Structures Vol.8 No.2
Factors dominating a mechanical behavior under compresive loads of stel structural members corrected by heating/presinghad been identified by using cruciform columns. These factors were geometric residual imperfection resulting from incompletecorrection by heating/presing and increase of yield stres due to large plastic deformation caused by local buckling and itscorection process. In this paper, in order to verify the generality of these factors, a series of experiments and the elastic-plasticlarge deformation analysis were carried out on box columns. From the results, the behavior under compresive loads such asgenerality of these dominant factors could be confirmed regardles of the structural shape of members.
Reaction Evaluation of Metal Surface Using Surface Potential Distribution Measurement
Youhei Hirohata,Ayumu Yokota,Kazuhiko Noda,Hideki Katayama,Hiroyuki Masuda 한국표면공학회 2010 한국표면공학회 학술발표회 초록집 Vol.2010 No.11
A surface potential measurement device with non-contact probe is applied to measure the potential of the passive metals. The surface potential distribution of high corrosion resistance materials shows difference behavior between titanium and type 304 stainless steel. From these results, the measurement of the surface potential using a surface potential measurement device is quite suitable to investigate the atmospheric corrosion behavior of high corrosion resistance materials.
Mikihito Hirohata,You-Chul Kim 한국강구조학회 2007 International Journal of Steel Structures Vol.7 No.3
by heating difered from that in virgin situation, the elastic-plastic large deformation analysis was carried out. When consideringonly residual imperfection, which was left through heating correction inevitably, the experimental phenomenon could not besimulated by the analysis. Then considering not only residual imperfection but also the increase of yield stres made by workhardening, which was caused by large plastic deformation, the experimental phenomenon could be simulated totally. From theresidual imperfection and the increase of yield stres made by work hardening.
Effects of Correction by Heating/Pressing on Mechanical Behavior of Steel Bridge Pier
Mikihito Hirohata,Takuya Morimoto,You-Chul Kim 한국강구조학회 2009 International Journal of Steel Structures Vol.9 No.1
A series of experiments was conducted in order to elucidate effects of correction by heating/pressing on mechanical behavior of steel bridge piers. Local buckling deformation of specimens due to loading considering the situation of an earthquake was corrected by heating/pressing, with or without water-cooling. Some out-of-plane deformations were inevitably left to avoid cracking in the welds. This geometric imperfection was defined as residual imperfection. After the correction, the same loading experiment was conducted. From the results, no deterioration was confirmed in mechanical properties of the steel even with water-cooling only if heating temperature was kept below A1 transformation temperature. Although it is ideal to have local buckling deformation repaired within the allowance of initial deflection in correction by heating/pressing, it was elucidated that making the residual imperfection mode opposite to local buckling mode was reasonable for guarantee of the maximum load of the corrected structure. A series of experiments was conducted in order to elucidate effects of correction by heating/pressing on mechanical behavior of steel bridge piers. Local buckling deformation of specimens due to loading considering the situation of an earthquake was corrected by heating/pressing, with or without water-cooling. Some out-of-plane deformations were inevitably left to avoid cracking in the welds. This geometric imperfection was defined as residual imperfection. After the correction, the same loading experiment was conducted. From the results, no deterioration was confirmed in mechanical properties of the steel even with water-cooling only if heating temperature was kept below A1 transformation temperature. Although it is ideal to have local buckling deformation repaired within the allowance of initial deflection in correction by heating/pressing, it was elucidated that making the residual imperfection mode opposite to local buckling mode was reasonable for guarantee of the maximum load of the corrected structure.