FATIGUE DAMAGE IN POLYCRYSTALLINE COPPER BELOW THE FATIGUE LIMIT

Surface fatigue damage was studied in polycrystalline copper cycled wi th constant plastic strain amplitudes below the fatigue limit. Fatigue damage in this interval of cyclic loading is manifested on the surfac e of the material as bands of localized cyclic slip: persistent slip b ands. They consist of extrusions and intrusions, and some of them also contain primary shallow cracks. The relative fraction of persistent s lip band volume close to the surface was taken as a measure of the sur face damage. The surface damage has been quantified in terms of the fr equency occurrence of the persistent slip bands as a function of lengt h and of the applied plastic strain amplitude. Characteristic paramete rs of the surface damage below the fatigue limit were evaluated.