Simulation of anisotropic crack growth behavior of nickel base alloys under thermomechanical fatigue

Abstract

Allvac®718Plus is a nickel base superalloy possessing outstanding abilities to withstand both mechanical and thermal loads, which make this material ideal for turbine disks and blades in aero engines. The thermomechanical fatigue (TMF) crack growth behavior depends on temperature, in-service load cycles and material orientation. In particular, the crack growth at high temperature dwell time shows significant influence of material anisotropy due to platelet-like precipitations, which leads to crack deflection from the maximum principal stress direction. These specific properties must be taken into account properly to ensure a safe design and the desired lifetime of components. The focus of this paper is to develop an appropriate fracture criterion to describe crack deflection for such kind of anisotropic material resistance. This criterion and the associated crack growth laws for thermomechanical fatigue are implemented in the FEM software Procrack for fully automated three-dimensional crack propagation simulation. The numerical simulation of experiments on CT-specimens with various material orientations provided evidence that the software can capture the actual fracture behavior. Moreover, a suitable set of material parameters could be identified. The performance of the presented approach to predict realistic three-dimensional TMF crack propagation is demonstrated by an application to a typical turbine component made from Allvac® 718Plus.