Two-Step Fatigue Tests on Pure Copper.

Polycrystalline copper specimens have been subjected to axial push-pull two-step fatigue tests in stress- and plastic strain controlled conditions. The differences between the amplitudes imposed under two-step loading as well as the block length of the program have been varied systematically. At the very moment the amplitude is changed in a test the material shows a characteristic deformation response nearly independent of the test duration. It is therefore concluded that the same deformation processes are involved - regardless of the test duration - and that they lead to comparable fatigue work hardening states. In tests with small differences between the two amplitudes the block length was observed to have no influence on the work hardening curve in contrast to tests with large differences in the amplitudes.