ON DETERMINING THE INTERNAL-STRESS USING HALL-PETCH DATA

Accurate evaluation of sigma(mu), the internal stress, is essential fo r determining sigma, the effective stress, because experimental yield stress data yield only the sum of sigma and sigma(mu). In the past, the most popular method of determining sigma(mu) has been the back ext rapolation technique which assumes that sigma = 0 at the now stress p lateau of a constant strain rate sigma vs. T plot, so that in this reg ion sigma = sigma(mu). Back extrapolating this cr, to absolute zero wh ile giving it the temperature dependence of the shear modulus was then assumed to determine sigma(mu) at temperatures below the plateau. Thi s technique has been shown to seriously overestimate sigma(mu) and und erestimate sigma and it has been shown that sigma(mu) may be measured more accurately [1,2,3] using strain rate sensitivity data. However, strain rate sensitivity data at sub-ambient temperatures are very diff icult to obtain accurately. This paper discusses another possible meth od for measuring sigma(mu) based on Hall-Fetch data, which appears to be much easier to use and of still greater accuracy.