PERSISTENT SLIP BANDS IN FATIGUED COPPER

Two series of copper single crystals, one of ‘0 5’ orientation and the other of [123] orientation, were fatigued in tension-compression over a range of constant stress amplitudes. Above a critical stress amplitude, a strong correlation was found between the strain amplitude and the fraction of the gauge area covered with persistent slip bands. Patterns etched on sections cut from a crystal could be matched to the pattern of persistent slip bands on the surface. These two results confirm that persistent slip bands are a surface indication of changes of dislocation structure within a crystal fatigued in tension-compression. The crystals displayed three types of fatigue behaviour as a function of stress amplitude, analogous to the S, F, and H stages defined by Wood and co-workers from the fatigue of crystals in torsion. Dislocation structures associated with persistent slip bands were studied by electron microscopy and found to be consistent with those observed by Lukáš and his collaborators. © 1969 Taylor & Francis Group, LLC.