Formation behavior of different topographies of crack growth path under high and low cyclic stresses in ultrafine-grained copper

Fatigue tests of ultrafine-grained copper specimens were conducted. The crack growth direction under constant stress depended on the magnitude of the stress amplitude. It occurred perpendicular to the loading axis at low stresses and was inclined at 45 degrees to the loading axis at high stress. To clarify the different growth mechanisms between the high- and low-stress amplitudes, two-step fatigue stress tests were conducted. The crack path formation under high- and low-stress amplitude is discussed from the viewpoint of the evolution of damaged areas around the crack. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.