The phase transition from visco-elasticity to plasticity. Description based on the generalized variational principle for dissipative continuum mechanics

It is shown in the report that the phase transition from the viscoelastic behavior of the medium to the plastic one can be described on the basis of generalized variational principle (GVP) for dissipative continuum mechanics in terms of nonlinear relaxation of internal microrotations of material points. The motion equations derived in the linear approximation on the basis of GVP correspond to the visco-elastic medium, a special case of which is the Maxwell’s medium with a low-frequency behavior as that of a conventional viscous fluid. It is shown how by only choice of the desired functional dependence of the shear nonlinearity it is possible to achieve the transition from the viscoelastic behavior of a medium to its plastic behavior with increasing of shear deformation.