Constitutive equation of plastic deformation of a zn-al alloy under tension-tension strain controlled cyclic loading

A constitutive equation of plastic deformation under tension-tension, strain controlled cyclic loading condition was derived from the transition state theory of rate processes. It was considered that the rate of plastic flow during the (tension-tension) cyclic deformation is controlled by a system of two consecutive energy barriers and that the material structural characteristics remain constant during cyclic deformation. The study revealed that within the stress, time, and temperature range, where the backward activations over the energy barriers are negligibly small, tension-tension, strain controlled cyclic deformation is essentially a stress relaxation process. The theory described well the cyclic deformation behavior of a near eutectoid ZnAl alloy. The constitutive parameters determined from the analysis of stress relaxation and tension-tension, strain controlled cyclic loading experimental results were identical. Consequently, it was recommended that stress relaxation can be used to determine the material structural characteristics which can then be used to predict the tension-tension, strain controlled cyclic deformation behavior of the alloy, using the constitutive equation derived in this report.