ON THE CREEP THEORY FOR THE STRAIN-HARDENING MATERIALS

The deformation process of the medium with full strains equaled to the sum of elastic and creep strains is considered. Elastic strains are described by Hook's law while creep strains velocities are functions of stress components and some structural parameters, velocities of their changing are described by Rabotnov's kinetic equations. It is assumed that Drucker's stability postulate in big, formulated for materials with time-depending behaviour, is valid for creep strains. The inversion of depends between stresses and strains as well as uniqueness of the solution of boundary value problems are discussed. A special case of aforementioned creep equations for a strengthening material, when the strengthening parameter is the value of specific scattered creep energy, is considered. The sufficient conditions for Drucker's stability postulate fulfillment in big are determined for this case, the reasons in favor of necessity of these conditions are given.