Prediction of the dimensional instability resulting from machining of residually stressed components

Residual stresses, built into most manufactured components, are revealed most dramatically during subsequent machining operations. Depending on the magnitude and distribution of the original residual stress state, the remaining part of a machined component distorts in order lo maintain the equilibrium of internal forces, resultng in a new state of residual stress distribution in the remaining material.

Given a known residual stress state in a material, the purpose of this research was to develop a methodology for the prediction of machining-induced distortions and the determination of the new state of residual stresses in the remaining material. In the first phase of this work, closed-form equations for the distortions of a residually stressed block, subjected to surface layer removal, were developed. Experimental and finite element simulations of the surface layer removal were also conducted and compared to the closed-form solutions.

In the second phase of this study, analytical solutions for the distortions and residual stress re-distribution in a cylinder subjected to machining of the inner surface were developed. The original residual stress state was determined by the elasto-plastic solution of a cylinder subjected to the autofrettage process as well as the finite element simulations of the autofrettage process. The effect of isotropic as well as cylindrically orthotropic material properties on the ensuing machining distortions and the redistributions of residual stress state were studied. Closed-form solutions and finite element results of this study demonstrated excellent agreement in the determination of distortions and the new state of residual stresses due to material removal operations.