On the eigenstrain application of shot-peened residual stresses within a crystal plasticity framework: Application to Ni-base superalloy specimens

• Imposed residual stresses within a crystal plasticity finite element framework.
• Implemented quasi-thermal expansion eigenstrain method.
• Explored microstructure heterogeneity effects on residual stresses variability.
• Good correlation obtained for scatter in the initial residual stress profile.
• Reproduced near surface trends in residual stress relaxation.

Shot-peening-induced compressive residual stresses are often introduced in Ni-base superalloy components to help prevent or retard surface fatigue crack initiation and early growth at near surface inclusions. In certain cases these compressive residual stresses can shift the fatigue crack initiation site from surface to sub-surface locations. However, the ability to computationally predict the improvement in fatigue life response and scatter due to induced compressive residual stresses are lightly treated in the literature. To address this issue, a method to incorporate shot-peened residual stresses within a 3D polycrystalline microstructure is introduced in this work. These residual stresses are induced by a distribution of fictitious or quasi-thermal expansion eigenstrain as a function of depth from the specimen surface. Two different material models are used, a J2 plasticity and a crystal plasticity model. First, the J2 plasticity model with combined isotropic and kinematic hardening is used to determine the distribution of quasi-thermal expansion eigenstrain as a function of depth from the surface necessary to induce the target residual stress profile within the microstructure. This distribution of quasi-thermal expansion eigenstrain is then used within a crystal plasticity framework to model the effect of microstructure heterogeneity on the variability in residual stresses among multiple instantiations. This model is verified with experimental X-ray diffraction (XRD) data for scatter in residual stresses for both the initial microstructure and after a single load/unload cycle.