Effects of residual stresses induced by repair welding on the fracture toughness of Ni-based IN939 alloy

Abstract

The present paper deals with the effects of repair welding residual stresses on the fracture behavior of IN939. A finite element (FE) model was developed using SYSWELD for the thermal-mechanical simulation of the welding process. The predicted residual stresses were verified through experiments. The results were then mapped to the fracture FE model in ABAQUS for further studies. A comparison of the fracture model predictions and experiments shows a reasonable agreement. The measured fracture toughness of partially welded compact tension (CT) specimens showed a considerable decrease in comparison with the as-received (AR) ones. The results revealed that welding residual stresses at the crack front were tangible non-uniform, and asymmetric. Both longitudinal and transverse residual stresses were maximum at the crack tip on free surfaces. In contrast, all three components of residual stresses were found to be compressive in the middle of the crack tip. The modified J-integral was affected by residual stresses and showed unexpected and irregular distribution along the crack front. Considerable changes were observed in both maximum J-integral value and its position. The residual stresses induced by the partial penetration repair welds reduce the fracture toughness, increase the crack driving force growth rate with the load, and change the critical point in which the crack driving force is maximum.