Growth mechanism of a small surface crack of ultrafine-grained copper in a high-cycle fatigue regime

High-cycle fatigue tests were carried out on specimens of ultrafine-grained copper produced by equal channel angular pressing. The growth behavior of a small surface crack was monitored. A major crack, which led to the final fracture of the specimen, initiated from shear bands. After initiation, the crack grew linearly in the shear direction of the final pressing. A decrease in growth rate with a change in growth path morphology occurred when the crack length reached l ∼ 0.1 mm. This decrease occurred because of a change in the crack growth mechanism and is explained by considering the interrelation between grain size and the reversible plastic zone size at the crack tip.