ELASTOPLASTIC RESPONSE OF PRESSURE-SENSITIVE SOLIDS

Tensorially invariant constitutive relations are systematically derive d for large strain elastoplastic response of geomaterials. The analysi s centres on Mohr-Coulomb (MC) and Drucker-Prager (DP) models with arb itrary hardening and non-associated response. Both flow and deformatio n theories are constructed for each model with emphasis on linear incr emental relations between the Eulerian strain rate tensor and the obje ctive Jaumann stress rate tensor. Specifying the results for plane str ain compression we find that deformation theory produces a much smalle r tangent instantaneous shear modulus than flow theory, It follows tha t failure of ellipticity and onset of surface instabilities predicted by deformation theory for associated solids occur at much lower levels of strain than the corresponding flow theory results. On the other ha nd, flow theory predictions admit a considerable sensitivity to the le vel of non-associativity. In fact, at high levels of non-associativity flow theory predictions for loss of ellipticity can be at strains bel ow those obtained from deformation theory. (C) 1997 by John Wiley & So ns, Ltd.