Plastic deformation of aluminum under repeated loading

The plastic deformation behavior of high purity (99.999 pct) polycrystalline and single crystal aluminum under repeated stressing was investigated by studying the creep behavior. The creep behavior under repeated stressing (cyclic creep) was compared with the static creep behavior at identical peak stresses. The influence of such experimental variables as the applied stress, the amplitude of cyclic stress, the test temperature and the static creep rate prior to stress cycling were systematically examined. The most important experimental observation in this study was that the cycling of the creep stress could either enhance or retard the creep deformation, depending upon the combination of the experimental variables. The experimental variable that had the most significant influence on the cyclic creep behavior was the applied stress; the enhancement of the creep rate was observed above a threshold stress, while the cyclic stress retarded the creep deformation at lower stresses. The threshold stress was found to depend sensitively on temperature. The implications of the threshold stress were examined by an analysis of the work-hardening behavior.