A new method for estimating residual stresses by instrumented sharp indentation

Abstract

A general methodology is proposed for the determination of surface residual stresses and residual plastic strains using instrumented sharp indentation. The residual stresses and the residual plastic strains are assumed to be equibiaxial and uniform over a depth (beneath the indented surface) which is at least several times larger than the indentation contact diameter. The indenter load and geometry can be so chosen as to minimize or maximize the contact radius to seek the broadest range of applicability and validity of the proposed method by recourse to macro-, micro- and nanoindentation of elastoplastic materials. Invoking the invariance of contact pressure in the presence of an elastic residual stress, or the change in the instantaneous yield strength of a strain-hardening elastoplastic solid in the presence of a residual plastic strain, a step-by-step method is outlined here to estimate pre-existing residual stress/strain fields. The technique can be directly used for residual stress measurements in such applications as thin films for microelectronics and optoelectronics, structural coatings, and engineered surfaces whose properties are altered by such methods as mechanical working, etching, ion implantation, case hardening, laser treatments, shot peening or laser shock peening. The predictions of the proposed analytical method for determining residual stresses have been shown to compare favorably with finite element predictions as well as available experimental results.