Overview of fatigue behavior in copper single crystals—I. Surface morphology and stage I crack initiation sites for tests at constant strain amplitude

Abstract The sharp-corner technique coupled with scanning electron microscopy has been used here for observing morphological changes at the surfaces of fatigued copper monocrystals. This technique confirms a number of recently-reported observations on persistent slip band (PSB) and crack initiation behavior, but elaborates others and provides new insights. For example, it reveals PSB encroachments (i.e. negative protrusions) which indicate that one mechanism of protrusion propagation is a shuttling mechanism amongs PSB-matrix lamellae. It is also found that there is a tendency to form longer cracks preferentially at the leading edges of positive protrusions and at the valleys of encroachments, implying that Stage I crack initiation sites are biased by the surface geometry. Interferometric observations show that PSB strain is inhomogeneous, being more highly localized at PSB-matrix interfaces, another phenomenon causing enhanced crack initiation.