NONASSOCIATED AND COUPLED FLOW RULES OF ELASTOPLASTICITY FOR ROCK-LIKE MATERIALS

Incremental elastoplastic stress-strain relations are studied which allow for non association of plastic strain rates with the (smooth) current yield surface (non-normality), and/or changing elastic moduli because of plastic deformations (elastoplastic coupling). These circumstances, often accompanied by strainsoftening, are significant in various geotechnical media, particularly rocks. On the basis of a suitable description of the rate relations, various ranges of the hardening modulus are established and their distinct behavioural characteristics, such as rate response uniqueness and material stability (or lack thereof) are systematically studied and interpreted in mechanical terms. Specialization to the standard compression tests and for particular forms of constitutive laws is made. Similarities to and differencies from the traditional associated flow rules of elastoplasticity are pointed out. © 1979.