Interaction of crack-tip constraint and welding residual stresses on the fracture behavior of Ni-based alloy

Abstract

The present paper aims to study the effect of crack-tip geometrical constraints and welding residual stresses (WRS), as well as their interaction on fracture behavior of IN939 superalloy, which is widely used in gas turbine hot section components, such as turbine vanes. For the thermal–mechanical simulation of welding processes, a finite element (FE) model was developed, and the predicted WRS was verified through experiments. Two welding paths and two mechanical boundary conditions were considered to develop four different WRS distributions within the same geometry. These results were mapped to the validated fracture finite element models. By varying the loading conditions, two sets of specimens with high and low geometrical constraints were achieved in the same geometry. Two-parameter fracture mechanics analyses were then used to examine the effects of four WRS profiles and geometrical constraints on the fracture behavior of each set. Generally, the impact of WRS is more evident in specimens with lower geometrical constraints. The fracture behavior might be unexpectedly affected if the WRS changes from tensile to compressive near the crack tip. Using the maximum stress triaxiality factor, it was shown that the fracture behavior as a function of WRS is better demonstrated than that of the Q-constraint parameter.