A MICROSTRUCTURALLY BASED METHOD FOR STRESS ESTIMATES

A method is described in which quantitative microstructural analysis i s used to estimate the local stress and strain states occurring within near-surface layers due to frictional contact. Quantitative estimates of local stress and strain have applications in friction and wear mod els, in finite element analysis of sliding interfaces, and as a basis for formulating and evaluating models on a local scale. This method is illustrated for three cases of dry sliding on nominally flat surfaces . Sliding tests were performed on a flat plate friction tester, develo ped at Sandia, which used copper friction samples and a steel test pla ten. The evolving friction coefficients were measured as a function of normal load and sliding speed. Microstructural analyses included both scanning and transmission electron microscopy (SEM and TEM) of the cr oss-sectioned friction samples. The sliding-induced dislocation substr uctures were quantitatively characterized and measured as a function o f subsurface depth and normal load. Two simple relationships between t he size scale of the dislocation substructure and the flow stress were used to estimate the material properties and the stress state as a fu nction of depth and normal load.