Metal Deformation Modeling—Stress Relaxation of Aluminum

Abstract

Experiments designed to test the validity of a model for rate-dependent inelastic deformation in metals are presented and discussed. The stress dependence of the strain rate in 99.99 percent pure aluminum was determined at 308 K from stress relaxation and creep experiments, and at 373 K from stress relaxation experiments. Deformation history was examined by conducting experiments subsequent to either monotonic tensile or reversed strain cyclic loading. At both temperatures and for both deformation histories, evidence of microstructural recovery was identified during the course of a relaxation experiment. The exponent characterizing recovery was found to be 20 at 308 K for both stress relaxation and creep; indicating that plastic deformation during creep and relaxation may be governed by the same kinetic law. The model is also found to predict correctly transient behavior observed in some relaxation experiments. This model apparently provides a physical basis for predicting relaxation subsequent to a variety of deformation conditions, thereby functioning as an evolutionary material law.