Eigenstrain Analysis of Synchrotron X-Ray Diffraction Measurement of Residual Strains in Machined Nickel Alloy Plates

Abstract

Manufacturing processes such as machining, surface treatment, welding, plastic forming, and stretching introduce permanent strains into workpieces and engineering components, leading to the creation of residual stresses. Residual stresses exert a significant influence on the deformation behaviour of components, e.g. inducing distortion during further machining, and also affecting their response to thermal and mechanical loading in service. This has important implications for dimensional stability and durability of components and engineering assemblies. In the present study a combined experimental and modelling analysis of a particular case of residual stresses induced in a nickel superalloy plate by heavy surface machining is presented. The residual elastic strain profile in the plate is determined using high-energy synchrotron diffraction. A variational procedure is then used to evaluate the underlying eigenstrain distribution responsible for the observed residual strain state. The relaxation of this residual strain state during subsequent sectioning of the plate is then considered. This example is used in order to assess the difference in the modelled residual strain and stress state obtained using three-dimensional, plane strain, and plane stress models of the coupon. The implications of these results for residual stress interpretation using eigenstrain procedures are discussed.