Abstract
Fatigue tests of ultrafine-grained copper plain specimens were conducted. The crack growth direction under constant stresses depended on the magnitude of the stress amplitudes. It occurred perpendicular to the loading axis at low stresses and was inclined at 45° to the loading axis at high stresses. 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 amplitudes was discussed from the viewpoint of microstructural evolution due to cyclic stressing.
