Residual stresses in rolled and machined nickel alloy plates: Synchrotron X-ray diffraction measurement and three-dimensional eigenstrain analysis

Most engineering components made from wrought metallic alloys undergo complex sequences of manufacturing operations. These processing steps frequently include extrusion, forging, or rolling, followed by machining and heat treatment. Since such components will be subjected to service loading as part of engineering assemblies, their durability must be assessed using suitably reliable life prediction models. The present study is aimed at the investigation of a combination of experimental and modelling techniques that involves microstructural investigation, diffraction measurement of residual elastic strains, and finite element simulation of residual stress distributions. Eigenstrain-based modelling approach to the analysis of processing-induced residual stresses has been previously presented in the two-dimensional approximation, i.e. under the assumption that the equivalent permanent plastic strain field induced by processing is equibiaxial. Several different formulations were considered and compared, including plane stress, plane stress, and three-dimensional models. In the present study a further development of the eigenstrain-based analysis approach that incorporates the experimental data obtained from synchrotron X-ray diffraction measurements of residual elastic strains in two complementary cross-sections of a forged and machined nickel superalloy plate is reported. The microstructure was assessed using electron backscattered diffraction, and near-surface residual stresses evaluated using laboratory X-ray diffraction. It is found that the results of fully three-dimensional formulation differ from two-dimensional approximations particularly in the vicinity of machined surfaces, having potentially significant implications for durability assessment and fatigue life models.