Theory of the Elasticity of Polycrystals with Viscous Grain Boundaries

Abstract

Previous experiments have shown that in annealed polycrystalline specimens, the grain boundaries are much more susceptible to plastic shear than are the interiors of the grains. This paper investigates the elastic properties of a specimen in which the grain boundaries are incapable of supporting shearing stresses. In such a specimen Young's modulus is found to be from 50 percent to 76 percent of its value when no slip at grain boundaries occurs, depending upon Poisson's ratio. This reduction of Young's modulus by slipping at grain boundaries should be observable by comparing values measured statically at elevated temperatures with those measured dynamically.