CYCLIC RESPONSE OF POLYCRYSTALLINE COPPER COMPOSITE-GRAIN MODEL

The cyclic deformation of polycrystalline f.c.c. metal is treated by v iewing differently-oriented grains as the components of a composite ma terial. Following a brief review of cyclic deformation in single- and polycrystals, a qualitative model of deformation behavior is developed by considering multi-slip regions to be relatively ''hard''. These re gions are of two kinds: (a) volumes adjacent to grain and twin boundar ies where multi-slip develops from compatability requirements, and (b) whole grains which happen to be favorably oriented for multi-slip bec ause of texture effects. The interiors of grains favorably oriented fo r single slip are considered as ''soft''. These considerations are val idated by the experimental fact that the substructure evolution observ ed in [111]-[100] textured copper seems to be better described if grai n-orientations are viewed in terms of the individual stress-state for each grain, and therefore the cyclic response of differently-oriented grains can be taken as that of the corresponding differently oriented single crystals. Finally, the model is shown to account qualitatively for some of the results reported previously from our laboratory: e.g. the differences in the cyclic response and levels of strain localizati on of fine-grained/weak-textured and coarse-grained/strong-textured co pper, and the absence of a plateau in the cyclic stress-strain curve o f fine-grained/weak-textured copper.