Fatigue life assessment of nickel-based single crystals considering equivalent initial flaw size model and anisotropy

Abstract

This paper presents a novel modeling framework for predicting fatigue life performance with varying film cooling holes (FCHs). Within this framework, in-situ crack propagation tests of nickel-based single-crystal plate specimens with two different drilling FCHs were carried out at room temperature. Based on the equivalent initial flaw size (EIFS) concept, a novel EIFS value proposed by modified Kitagawa-Takahashi diagram method for plastic correction of anisotropic Hill criterion, and the initial fatigue quality of these two types of FCHs was quantitatively evaluated and verified using surface integrity detection. Subsequently, the EIFS value with 95% confidence and 95% reliability (EIFS95/95) was obtained, which considered the data dispersion. The anisotropic equivalent stress-intensity factor ΔKeq calculated by the crystal slip theory is used to describe the mixed fracture mode under the action of KI, KII, and KIII. In addition, a novel fatigue-crack growth function with EIFS95/95 is proposed, which can effectively describe the actual crack growth behavior. Finally, combined with the EIFS and fatigue crack rate, considering the values of two stress intensity factor thresholds for testing different survival rates, a robust fatigue-life prediction results within the range of twice error bands were in significant agreement with the experimental results.