On the material symmetry group for micromorphic media with applications to granular materials

Within the framework of the theory of nonlinear elastic micromorphic continua we introduce the new definition of the local material symmetry group. The group consists of ordered triples of second- and third-order tensors describing such changes of a reference placement that cannot be recognized with any experiment. Using the definition we characterize the micromorphic isotropic media, micromorphic fluids, solids and special intermediate cases called micromorphic subfluids or micromorphic liquid crystals. We demonstrate that some typical behaviour of such complex media as granular materials can be described within the micromorphic subfluids mechanics.