A microstructurally based method for stress estimates

A method is described in which quantitative microstructural analysis is 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 models, 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, developed at Sandia, which used copper friction samples and a steel test platen. 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 cross-sectioned friction samples. The sliding-induced dislocation substructures were quantitatively characterized and measured as a function of subsurface depth and normal load. Two simple relationships between the size scale of the dislocation substructure and the flow stress were used to estimate the material properties and the stress state as a function of depth and normal load.