厚板補修溶接部の力学的特性 ３次元溶接残留応力・残留塑性ひずみ分布の特徴とそれらの生成機構

Abstract

Repair welding produces welding deformation, residual stresses, etc. which may newly produce repair welding cracks. Therefore, it is important to clarify the mechanical characteristics of repair welds in thick plates.In this paper, three-dimensional unsteady thermal conduction analysis and three-dimensional thermal elasto-plastic analysis are performed. Based on the results, study is made on the characteristics of distributions of three-dimensional welding residual stresses and plastic strains, and their production mechanisms. The main conclusions can be summarized as follows :1) Residual stresses and plastic strains in the base plate are largely affected by compressive hydrostatic stresses and compressive plastic strains produced in the heating stage, respectively. This is remarkable in the base plate near HAZ.2) Irrespective of elastic or plastic, severity of mechanical restraints in respective directions can be known from the magnitude of produced stress components, {σx, σy, σz)T.3) Since plastic strains are assumed to be incompressive, the sign of plastic strain produced in the direction where maximum stress is produced (mechanical restraint is the severest) is opposite to that in the direction where minimum stress is produced (mechanical restraint is the weakest). Accordingly, the signs of stress and plastic strain may disagree.4) For evalution of mechanical damage of the material suffered from welding, it is necessary to pay attention to the whole process of a series of elasto-plastic behaviors, not only to the magnitude of residual plastic strains. In this paper, plastic work is proposed as a parameter to evalute the severity of mechanical condition including transient state in the plastic region. The plastic work becomes maximum in the base plate near HAZ.