High cycle fatigue life prediction model based on crystal plasticity and continuum damage mechanics for Ni-based single crystal superalloys under a multiaxial stress state

Abstract

A high cycle fatigue life prediction model based on continuum damage mechanics, crystal plasticity and critical distance theory is developed. A novel damage evolution law for anisotropic Ni-based single crystal materials built on continuum damage mechanics is proposed. The crystal plasticity framework was introduced to take into account the particular characteristics of high cycle fatigue. The critical distance theory was innovatively applied to the structure of film cooling holes to predict the lifetime for materials under a multiaxial stress state. High cycle fatigue tests considering drilling technology, stress ratio and creep time were performed using Ni-based single crystal superalloy plates with film cooling holes. The constitutive equations were implemented into a finite element framework to simulate the high cycle fatigue properties of Ni-based single crystal superalloys, and the results of numerical calculations were compared with experimental observations. It was demonstrated that the constitutive formulations proposed in the present study can be used to model the mechanical behavior of Ni-based single crystal superalloys under a multiaxial stress state. The life prediction errors are found to be within the factor-of-three scatter band. The fatigue life of the specimen with ultrafast laser drilled film cooling holes is larger than that with electrostream machined film cooling holes under the same test conditions. The fatigue strength of the specimen with film cooling holes at a stress ratio R = 0.95 is higher than that at a stress ratio R = -1. The life of the specimen with film cooling holes is found to decrease with increasing creep time before high cycle fatigue. The γ/γ'-microstructure evolution in the specimens with film cooling holes is related to the kinetics of the stress redistribution during the fatigue process. A minimum stress level is essential for rafting to occur. The damage distribution for the plate model is in line with the crack initiation location and propagation region of the specimen.