J-Integral Estimation for the 3-D Through-Thickness Centre-Cracks in Welds of Structural Steels

Abstract

For the fracture analysis of a crack in welds, residual stress analysis and fracture mechanics analysis must be performed sequentially. In this study, characteristics of residual stresses in welds of structural steels (SM490, SM520, SM570) were presented by carrying out three-dimensional (3-D) thermal elastic-plastic finite element (FE) analysis. Then, an FE analysis method which was able to calculate domain-independent values of the J-integral for a crack in a 3-D residual stress bearing body was developed to evaluate the J-integral for a mode-I centre-crack in welds of structural steels when mechanical stresses were applied in conjunction with residual stresses. The results show that the longitudinal residual stresses in welds increase with increasing yield stress of the welded steel (SM490<SM520<SM570). For the through-thickness centre-cracks in welds of structural steels where only residual stresses are present, the J-integral values increase with increasing yield stress of the welded steel. This is because the longitudinal residual stresses in welds, which in this case act as the crack driving force, increase with increasing yield stress of the welded steel. Furthermore, the values of the J-integral for the case when mechanical stresses, applied in conjunction with residual stresses, are larger than those for the case when only residual stresses are present. This is because tensile stresses by mechanical loading are added to the existing residual stresses; hence the crack driving force is larger.