Determination of residual surface stresses with the aid of resistance wire strain gauges

Summary

A method due to Stäblein for determining surface residual stresses is modified. For stress determination thin layers of an initially flat test bar are polished away. Instead of measuring the change in curvature, the change in strain on the surface opposite the removed layers is measured with a resistance wire strain gauge. From the assumptions that the residual stresses are constant in-surfaces parallel with the polished one and that the transverse and thickness stresses can be neglected, an expression is derived connecting change in strain with initial residual stress in the bar. As an example of the practical application of the method described the results of a determination of the residual surface stresses in a case-hardening gear tooth steel are reported.