Research On Damage Behavior Of Welded Joints Containing Defects And Engineering Calculation Method Of Damage Parameters

Welding is a process in which not only occurs non-uniform thermal cycling but also complicated physical and chemical metallurgy, thus there exist remarkable organize gradient and mechanical heterogeneity in welding joints. It is doubtless that the research on damage behavior and engineering calculation method of damage parameters of weldments with mechanical heterogeneity is practically significant for the assessment of the integrity of welded structures.In this paper, based on the UMAT technique of ABAQUS and a fully coupled strain and isotropic damage elasto-plastic constitutive equations, a finite element code is developed to simulate the elasto-plastic damage behaviors, fracture behaviors and fracture mechanical parameters of weldments with mechanical heterogeneity. Therefore, the effects of mechanical heterogeneity, such as strength matching, rupture strain matching and strain-hardening parameter matching, on the damage evolution and the relationship between damage parameter and fracture mechanical parameter are analyzed in detail by taking welded specimens containing crack in weld, HAZ or fusion line as the object investigated. In addition, the author carried out a preliminary exploration for the engineering calculation of damage parameters.The comparison between the calculated and experimental results indicates that the UMAT procedure developed in this paper can simulate the mechanical properties of structures with damage exactly, and improve the shortcomings of the common elastic-plastic model which overestimate the tensile strength of welded joints. The damage behaviors, fracture behaviors and the relation between damage parameter and fracture parameter(J-integral, CMOD) are affected markedly by mechanical heterogeneity for all kinds of welding joint with cracks in different zones. That is, the higher the strength matching, base metal rupture strain, and base metal strain-hardening parameter are, the lower the damage parameter, J-integral and CMOD are.On the other hand, an engineering calculation method of damage parameter which has arrived at a certain credibility were established for the welded joints with cracks in the weld by means of fitting, based on the analyses of the calculation results previously.