A NEW METHOD FOR ESTIMATING RESIDUAL-STRESSES BY INSTRUMENTED SHARP INDENTATION

A general methodology is proposed for the determination of surface res idual stresses and residual plastic strains using instrumented sharp i ndentation. The residual stresses and the residual plastic strains are assumed to be equibiaxial and uniform over a depth (beneath the inden ted surface) which is at least several times larger than the indentati on contact diameter. The indenter load and geometry can be so chosen a s to minimize or maximize the contact radius to seek the broadest rang e of applicability and validity of the proposed method by recourse to macro-, micro- and nanoindentation of elastoplastic materials. Invokin g the invariance of contact pressure in the presence of an elastic res idual stress, or the change in the instantaneous yield strength of a s train-hardening elastoplastic solid in the presence of a residual plas tic strain, a step-by-step method is outlined here to estimate pre-exi sting residual stress/strain fields. The technique can be directly use d for residual stress measurements in such applications as thin films for microelectronics and optoelectronics, structural coatings, and eng ineered surfaces whose properties are altered by such methods as mecha nical working, etching, ion implantation, case hardening, laser treatm ents, shot peening or laser shock peening. The predictions of the prop osed analytical method for determining residual stresses have been sho wn to compare favorably with finite element predictions as well as ava ilable experimental results. (C) 1998 Acta Melallurgica Inc. Published by Elsevier Science Lid. All rights reserved.