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 AMI nickel-based single crystal superalloy. The Ortner method is used to determine residual elastic stress depth profiles in plane-parallel samples. They exhibit a I30-I60 µm thick hardened layer where there are compressive stresses up to 1000-I400 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.

Influence of residual stress distribution and microstructural characteristics on fatigue failure mechanism in Ni‐based Superalloy

“…Several researchers reported the influence of residual stresses and its stability on fatigue performance of materials. [10][11][12][13] For example, Doremus et al 14 reported that residual stresses delay the crack growth during the first stage of propagation as compared to long crack growth indent type surface anomalies and also affect the crack front shape. Dalaei et al 15 reported that a significant improvement in fatigue life can be expected as long as surface residual stresses are higher than the 50% of stress amplitude at half of the lifetime.…”

“…Several researchers reported the influence of residual stresses and its stability on fatigue performance of materials 10–13 . For example, Doremus et al 14 reported that residual stresses delay the crack growth during the first stage of propagation as compared to long crack growth indent type surface anomalies and also affect the crack front shape.…”

Investigations into the Surface Strain/Stress State in a Single-Crystal Superalloy via XRD Characterization

“…This conclusion is consistent with the observation of the anomalous rafting in this zone. Amélie Morançais et al [19] researched the effect of shot-peening on the low-cycle fatigue life of AM1 superalloy by XRD. Compressive stresses of up to 1000-1400 MPa were found on the surface layer by XRD.…”