DEFORMATION MODELING OF MULTIPHASE POLYCRYSTALS - CASE OF A QUARTZ MICA AGGREGATE

Many materials, including rocks, are composed of different phases with stronger and weaker components. In order to investigate such systems and the interaction between phases and their influences on texture development, we have developed a viscoplastic self-consistent scheme in which a microstructure is prescribed and grains are divided into cells so that different parts of a grain can deform differently. The system used as an example is quartz and mica. A pure quartz polycrystal is compared with a 75% quartz-25% mica mixture. Quartz deforms by prismatic, basal and pyramidal slip, and platelets of mica are assumed to be largely rigid. If quartz grains are forced to deform homogeneously, the predicted quartz texture becomes stronger when mica is added because the sample strain is accommodated only by the quartz. This is contrary to experimental evidence. However, if quartz grains are allowed to deform heterogeneously, as controlled by neighbor interactions, the predicted quartz texture becomes weaker when mica is added. Such a model with intragranular heterogeneity may describe the real behavior of two-phase mixtures and is also compatible with observed microstructures which document considerable grain bending of the weaker phase around grains of the more rigid phase.