Variant of thermoviscoplasticity theory

Basic terms and equations of the theory of thermoviscoplasticity (inelasticity) belonging to the class of theories of flow in combined hardening are discussed. The tensor of strain rates is presented as a sum of tensors of the velocities of elastic and inelastic deformations. It should be noted that in this theory there is no conventional separation of the inelastic strain for deformation plasticity and creep. Elastic strain follows the generalized Hooke's law common to non-isothermal loading. The authors introduce a yield surface which isotropically expands or contracts and shifts to the process of loading. The current yield surface is defined by the process loading. The impact of the time factor is the process of loading too. For the radius of the yield surface it became possible to formulate the evolution equation that takes into account additional isotropic hardening under non-proportional (complex) load; and it is also generalized to non-isothermal loading processes and return to mechanical properties after annealing. We accepted parameter Kadashevich-Mosolov (corresponding to the angle between the velocity vectors of strain and stress) as a parameter describing a measure of the complexity of the process of loading,. The displacement yield surface is described on the basis of Novozhilov-Suboshi implying that the total displacement is the sum of displacements; each of them is its evolution equation. The analysis of hysteresis loops of plastic has allowed to allocate three types of microstresses (displacements) and formulate three types of evolution equations generalized to non-isothermal loading processes and relieving of microstresses during annealing. To determine the rate tensor of inelastic deformation we use the associated (gradiently) law of flow. For hard and soft loading regimes, the expressions for determining the rate of the accumulated inelastic deformation were found. The terms of elastic and inelastic states are formulated. To describe the nonlinear process of damage accumulation we introduced the kinetic equation of damage accumulation, where the energy that is required to create damage in the material is taken as the energy equal to the work of microstresses of the second type on the field of inelastic deformations. Here these kinetic equations are generalized to non-isothermal loading and the processes of embrittlement and heal the damage. Material functions closing the theory variant are specified, the basic experiment and method of identification of material functions are formulated. The description of the verification version of the theory of thermoviscoplasticity on a wide range of structural steels and alloys and programmes of experimental research are presented.