Influence of Residual Stresses on the Fatigue Life of a Shot-Peened Nickel-Based Single Crystal Superalloy: From Measurements to Modeling

Abstract

In this work, X-ray diffraction measurements and finite elements calculations are combined to investigate the effect of the shot-peening process on the fatigue lifetime of the AM1 nickel-based single crystal superalloy. The Ortner method is used to determine residual elastic stress depth profiles in plane-parallel samples. They exhibit a 130-160 μm thick hardened layer where there are compressive stresses up to 1000-1400 MPa. The tensile stresses which ensure the mechanical equilibrium of the samples are not localized in a specific layer but rather distributed in a few millimeters thick layer. The eigenstrain theory is then used to incorporate measured stresses in the elasto-viscoplatic modeling of shot-peened fatigue test specimens. A numerical method is proposed to initialize hardening variables in the shot-peened layer independently of the complexity of the constitutive law or measurements in calibration samples. Finally, a fatigue analysis at 650 • C is performed in samples with a stress-concentration. The effect of shot-peening on the fatigue lifetime is studied using both modeling and measurements. Results are in good agreement in the investigated range of applied stresses. However, measurements show that residual stresses from shot peening are not always beneficial.