CONFIGURATIONAL ENTROPY, NON-ASSOCIATIVITY AND UNIQUENESS IN GRANULARMEDIA

It has long been recognized that fabric, i.e., the grain configuration in a domain, plays a significant role in the constitutive response of granular media. Here we establish that this effect has bearing on the suitability of non-associative plasticity laws that describe the obse rved deviation of the plastic strain rate, from the normal to the yiel d surface. It is known that when non-associated plasticity laws are us ed, uniqueness of the solution of the initial value problem cannot be proved. Here it is shown that the introduction of configurational entr opy and temperature into the theory, gives rise to a thermodynamic fra mework, specifically a thermoplastic potential, with respect to which the plasticity law is associative. However, the inelastic strain is th e sum of a plastic and a configurational strain. While the plastic str ain rate is still normal to the potential (yield) surface, the inelast ic strain rate, which is what is measured in the laboratory, is not. I t is further shown that despite the non-normality of the inelastic str ain rate to the plastic potential surface, the solution of the coupled initial value - configurational diffusion problem is unique. In the p rocess of development of the underlying configurational thermodynamics , the concept of configurational flux is introduced and a time indiffe rent configurational diffusion law is inferred on the basis of uniquen ess requirements. Thus the foundation is laid for the mode of propagat ion of chaos in granular media.