CREEP STIMULATED BY INTERRUPTED LOADING IN COPPER AND COPPER-1-PERCENT-CADMIUM

Creep can be induced by cyclic loading in many metals and alloys. In this work the results of experiments on copper and a copper-1% cadmium alloy are described in which the creep produced by cyclic loading was compared with that occurring under a static load. Creep in copper can be stimulated by interrupted loading and two stages of induced creep were distinguished. The first stage is believed to be an extension of the Kennedy effect, in which rapid recovery in the unloaded state is produced by the cross-slip of screw dislocations. In the second stage more extensive recovery occurs, probably involving climb of edge dislocations. The magnitude of the induced creep is mainly determined by the relationship between the flow stress, the applied stress and the stress removed on unloading. The results are discussed in terms of a simple model involving these three factors. In contrast, the copper-1% cadmium alloy was generally observed to be much more resistant to cyclic loading (probably because of strain aging) although at large applied loads sudden increments in strain were observed after about 50 h of load cycling. © 1979.