SECOND-ORDER PLASTIC FLOW OF ISOTROPIC PARTIALLY COMPRESSIBLE MEDIA.

Using tensorial expansions, the author derives yield criteria and rules for the second-order plastic flow of partially compressible media. The strain-rate tensor is considered as an isotropic tensorial function of the material-stress tensor. The flow rule is obtained from the tensorial expansion of this function in the form of a three-terms formula. Yield criteria are derived from the increments of the strain energy or of the material strain energy, respectively. The hypothesis of constant limiting invariant quotients is introduced. The derived yield criteria for the second-order plastic flow are of the third degree. Yield criteria and flow rules contain four material constants, namely three limiting invariant quotients and the material coefficient, which are determined from particular limiting states in terms of particular yield stresses.