Finite element analysis of a notch root semi-elliptical crack in single crystal superalloy

Abstract

In this article, the stress/strain concentrations at a notch and the J integral of a semi-elliptical crack embedded at the notch root in a single notch bar of single crystal (SC) superalloy PWA 1480 are studied, using finite element method (FEM). Two material orientations, [0 0 1]/[1 0 0] and [0 0 1]/[1 1 0] (loading/notch directions), have been evaluated to study the effect of material anisotropy on the aforementioned fracture mechanics quantities. In the present study, only the case of mode I cracking is considered with a tensile load applied in the longitudinal direction of the notched bar. The elastic–perfectly-plastic condition is assumed for the material, such a behavior would particularly occur at the notch root. Coupling the elastic–perfectly-plastic condition with the Hill’s function for the yield potential, the material model considers anisotropic yielding but without strain hardening at the post-yield stage. Four load cases for three different crack sizes with the same aspect ratio are analyzed. The effect of material anisotropy on both J integral and crack tip opening displacement (CTOD) are discussed and compared with that of isotropic materials. A correlation is also established between the J integrals of a semi-elliptical crack and that of a through-the-thickness crack evaluated based on the continuously distributed dislocation theory.