Elastic-plastic FE calculations for a fracture mechanics analysis of a weld in the ligament of a CT specimen

Abstract

Results of elastic-plastic FE calculations on four plane strain models of a CT-100 specimen, (a) with a weld in the ligament, (b) of base material only, (c) of welding simulated material only and (d) of weld material only, are compared and discussed in the light of fracture mechanics aspects. Regarding the cleavage fracture regime, considerably higher crack opening stresses are obtained in the welded specimen than in the base material specimen, as soon as small-scale yielding occurs. Conservative evaluation of the crack opening stresses of the welded joint can be achieved by using the welding simulated material properties. The J- integrals determined by the energy release rate using the method of virtual crack extension are equal for the four material models up to about 200 N mm −1. Above this level, the behaviour of the welded specimen and that of the base material model are still similar, while a higher force is necessary for the welding simulated material model and the weld material model to reach the same J- value as for the two others. The crack opening profile of the welded specimen is asymmetric to the fusion line which lies in the ligament. The half profile of the heat-affected zone side is comparable to that of the welding simulated material model and the half profile of the weld material side to that of the base material model. A higher maximum of the equivalent strain on the heat-affected zone side than on the weld material side may explain why cracks tend to run into the base material region of the weld under conditions of stable crack growth. General yield of the welded specimen occurs on the base material side, whereas on the weld material side only a small plastic zone is visible, comparable to that in welding simulated material at the same load.