Surface and size effects in unloading yield point

Abstract

The removal of a surface envelope by chemical polishing of an unloaded crystal, previously deformed plastically in tension, is shown to reduce the unloading yield point. In addition it is shown that the yield point changes continuously with stress and a maximum effect is obtained at a given stress which depends on the crystal size. Furthermore the value of the maximum is a function of crystal size. On the basis of these results it is argued that the unloading yield point can probably be attributed to the non-uniform flow stress distribution which exists near the surface in deformed crystals.