ON THE NUCLEATION OF PERSISTENT SLIP BANDS IN FATIGUED COPPER SINGLE-CRYSTALS

The onset of strain localization in a copper single crystal oriented for single slip and cycled at a constant plastic strain amplitude corresponding to the low end of the plateau in the cyclic stress-strain curve has been explored by interferometry and analysis of hysteresis loops. Current methods for analyzing behavior early in life are shown to be inadequate. Several new methods involving the shape of the hysteresis loops are introduced. Changes in local curvature have been observed throughout rapid hardening. The nucleation of persistent slip bands coincides with a basic change in the shape of the hysteresis loops.