On newtonian viscoplastic dislocation creep and the effect of the Peierls stress

Abstract

Single crystals of synthetic quartz have been deformed in a uniaxial rig without a confining pressure, and a mechanical steady state has been observed. Using the new results on quartz, together with those on metals and ceramics published in the literature, it is demonstrated that crystalline materials may deform by newtonian dislocation creep with a threshold stress σ c under certain conditions. This newtonian viscoplastic ( σ c ≠ 0) behavior may not be recognized if the conventional power law creep equation under the assumption of σ c = 0 is applied to describe the experimental data. Observations on metals, ceramics and silicates suggest that the identified newtonian viscoplastic dislocation creep operates at stresses larger than the Peierls stress and that the threshold stress may originate from the lower limiting stress required to cause dislocation glide. The newtonian viscoplastic dislocation creep proposed herein is different from the classical Harper-Dorn creep which operates at stresses lower than the Peierls stress.