A FAMILY OF YIELD LOCI BASED ON MICRO MECHANICS

G. R. MCDOWELL

ABSTRACT: This paper examines a recently proposed work equation which accounts for energy dissipated in particle fracture nd frictional rearrangement. A simple approach is adopted whereby the relative proportion of plastic work dissiated in fracture and friction is a simple function of stress ratio, and the normality principle is applied to generate a ew family of yield loci. The derived family of yield loci requires the specification of a single parameter in addition to Lie critical state friction dissipation constant, and the original Cam clay yield locus is shown to be a special member of his family. By selecting an appropriate value of the new parameter, it is possible to model many of yield surfaces commonly encountered for isotropically consolidated clays and sands. The method also provides a convenient way of rounding off the corner of the Cam clay yield locus, if that is all that is required. The approach is useful in that it warns against use of the new yield loci on the dry side of critical states: for this purpose a non-continuum approach should be used. Care should also be taken in applying the normality principle: for sands at high stress ratios, extensive article rearrangement occurs, in which case a non-associated flow rule could be adopted with the new family of loci.

key words: constitutive relations, fracture, friction, micro mechanics, plasticity (IGC: D6)