The Role of Internal Stress in the High-Temperature Deformation of Copper

Polycrystalline copper of 99·99% purity has been deformed in tensile creep at a variety of strain rates and temperatures. The internal stress developed during creep deformation was measured by a modified stress-relaxation technique. The magnitude of the internal stress remains constant during steady-state deformation but the ratio of internal stress to applied stress depends critically on the creep rate and test temperature. At low creep rates the internal stress closely approaches the value of the applied stress but as the creep rate increases the magnitude of the effective stress becomes greater. The magnitude of the internal stress is related to the scale and nature of the dislocation substructure.