Cyclic creep acceleration and retardation in polycrystalline copper tested at ambient temperature

Abstract

In order to understand the mechanisms of cyclic creep retardation and acceleration, tests in both static and cyclic creep have been made on copper polycrystals at ambient temperature. Cyclic retardation occurs at low stress and acceleration at high stress. An expression for the temperature dependence of the threshold stress for acceleration is offered. The dislocation structures of the cyclically-crept copper have also been explored both in the presence and absence of strain bursts, and as a function of stress amplitude and grain orientation. Cyclic creep acceleration is interpreted by a cyclic softening process involving dislocations on secondary systems, and the role of point defects is discounted.