CYCLIC RESPONSE OF POLYCRYSTALLINE COPPER COMPOSITE-GRAIN MODEL

The cyclic deformation of polycrystalline f.c.c. metal is treated by viewing differently-oriented grains as the components of a composite material. 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 regions are of two kinds: (a) volumes adjacent to grain and twin boundaries where multi-slip develops from compatability requirements, and (b) whole grains which happen to be favorably oriented for multi-slip because of texture effects. The interiors of grains favorably oriented for single slip are considered as ''soft''. These considerations are validated by the experimental fact that the substructure evolution observed in [111]-[100] textured copper seems to be better described if grain-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 localization of fine-grained/weak-textured and coarse-grained/strong-textured copper, and the absence of a plateau in the cyclic stress-strain curve of fine-grained/weak-textured copper.