Growth Path of Small Surface-Cracks in Ultrafine GrainedCopper under Cyclic Loading

High-cycle fatigue tests were carried out on specimens of ultrafinegrained copper produced by equal channel angular pressing. The formation behavior ofsurface damage and the growth behavior of a small surface-crack were monitored. Amajor crack, which led to the final fracture of the specimen, initiated from shear bands(SBs). Propagation behavior of the major crack was influenced by damage ahead of thecrack tip, and consequently different morphologies of the crack growth paths developed,depending on the stress amplitude. The physical background of growth path formationwas discussed from the viewpoint of the evolution of surface damage.