ANALOG EXPERIMENTS AND NUMERICAL MODELING ON THE RELATION BETWEEN MICROGEOMETRY AND FLOW PROPERTIES OF POLYPHASE MATERIALS

Constant stress experiments, with shear strains of up to 185, were carried out with two-phase composites of power-law creep organic crystalline rock analogues: camphor and octachloropropane (OCP). Isotropic mixtures of camphor inclusions (hard) in an OCP matrix (soft) show initial softening coinciding with the development of foliation, followed by hardening coinciding with buckling and folding of the camphor foliation. A mixture of OCP inclusions in a camphor matrix softens rapidly while shear is localized by linking of the soft OCP inclusions at a bulk shear strain of less than unity. Numerical modelling shows that the fraction at which the phases change their roles of connected phase and the inclusion phase seems to be the most important parameter for relating the microgeometry to the composite flow properties. The connectivity changes as the microgeometry evolves during deformation. Therefore the properties of a polyphase material change during deformation, as was observed with the analogue experiments. These changes may lead to localization of deformation in shear zones.