A simple model of uniaxial creep recovery and stress relaxation based on residual-stress redistribution

Abstract

A useful and simple model describing primary creep, creep recovery, and stress relaxation is put forward. The model is based on the concept that creep recovery and stress relaxation occur as a result of the redistribution of internal stresses within materials. These internal stresses result from the inhomogeneity of crystalline materials on a microscopic scale, the stresses being attributed to the constraints between neighbouring grains, to the coherency strains associated with solute atoms and second-phase particles, and to dislocation interactions. It is shown that the model satisfactorily describes the creep-recovery and stress-relaxation properties of commercially pure copper. It also predicts a number of other experimental observations. These are (1) that creep strain recovered will be proportional to the originally applied stress and less, in most circumstances, than the initial elastic loading strain, (2) that creep recovery in single crystals of pure metals will be negligible, and (3) that creep recovery in highly alloyed materials will be greater than in relatively pure metals. The analysis is limited to loading within the elastic range, but this is not an essential feature of the model and the effects of plastic strain on loading are discussed.