Mathematical theory of plasticity for frictional materials

We consider the extension of the classical mathematical theory of plasticity to frictional materials. It is shown that the apparently nonassociated plastic flow characteristics often observed in such materials can be accounted for by models that are variational in structure. In addition, the theory predicts a number of new terms and functional relationships that appear to have particular relevance to granular materials. The theory is illustrated by the construction and calibration of a simple five-parameter model for sands.