Abstract
The predictions of the Ashby equation for the increase in polycrystal work hardening over that which occurs in single crystals have been compared with stress-strain measurements as a function of grain size for copper and 70–30 brass. The Ashby equation does not apply above ϵ = 0·01 in either material; in copper the equation is quantitatively incorrect below ϵ = 0·01; in brass Lüders strains prevented an examination of behaviour below ϵ = 0·01. These results support a previous suggestion that the Ashby model for grain boundary hardening requires revision.