厚板補修溶接部の力学的特性 ＩＩ ３次元熱弾塑性問題の平面変形問題への置換の可能性の検討

Abstract

In this paper, a model of repair welds is assumed for three-dimensional thermal elasto-plastic and two-dimensional plane-deformation thermal elasto-plastic analyses. The results of the analyses are compared in order to clear and to consider the mechanism necessary for replacing three-dimensional problems with plane-deformation problems.Thesummaryofthemainconclusionsisasfollows:Promtheresultsofthree-dimensionalthermalelasto-plasticanalyses;1) In the portion which undergoes a quasi-steady state temperature history, whether there is temperature gradient along the weld line or not, the producing residual stresses and plastic strains are same at each cross section along weld line if the rigidity to thermal shrinkage is uniform.2) The shorter of the length of repair weld and the slower of travel speed, the more stress component of perpendicular to weld line, σy, increases. Moreover, the plastification is delayed by slow travel speed, so that plastic strain component of welding direction, epx decreases.From the comparison between the results of two-dimensional plane-deformation and three-dimensional analyses3) Only when the weld length is long and there is no temperature gradient along the weld, three-dimensional problems can, in the strict sense of production mechanism, be replaced plane-deformation problems including the distribution and magnitude of transient and residual stresses and plastic strains. However, as residual stresses are controlled by the yield condition of a material, replacement of the three-dimensional problems with plane-deformation problems leads to estimation of the distribution and magnitude without large difference in the results. If the travel speed is decreased, it needs to be paid attention to underestimate σy, in plane-deformation analysis. Whereas, since the distribution and magnitude of plastic strains are largely affected by the mechanical boundary conditions, the estimation of plastic strains are less accurate than that of residual stresses in plane-deformation analysis.4) The temperature distribution for thermal elasto-plastic stress analysis of plane-deformation can be given from two-dimensional analysis which assumes no thermal conduction from the cross section.5) According to the model, if the travel speed is v≥0.0055 m/s in the portion which undergoes quasisteady state until it cools down to 400°C (the weld length; l≥0.2 m, at least the middle parts of model undergoes quasi-steady state), the distribution and magnitude of residual stresses and plastic strains can be estimated from plane-deformation analysis. When only residual stresses are needed to be known, ν≥0.0017 m/s may be enough for the plane-deformation analysis to work out.