Simulation of residual stresses during pulsed thermo-force surface hardening

The paper deals with solving the mechanic connected problems applying to residual stresses under non-stationary thermal effects. The research is aimed at the electromechanical processing technology in the application to titanium pseudo-α-alloys which change their phase composition due to the martensitic phase transition under local thermal effects on the surface layer. The paper provides a mathematical formulation, considered features and methods for solving a thermostable contact problem inclusive of the phase transformations occurring during high-speed cooling. The main stages of building the necessary defining relations are shown. Relevant correlations of the plastic flow theory in the velocity form in the limits of the isotropic-translational hardening model are given, issues of integrating these correlations are considered. The technique determining the non-stationary contact zone of an absolutely rigid stamp and a deformable half-space is shown. The main linearization stages of the variational equation used are considered separately. Within the developed algorithm, a series of computational experiments were made simulating the temperature-force effect in Ti6Al2V titanium pseudo-α-alloy as applied to the technology of the pulsed thermal-force surface hardening. It is established that the electromechanical surface treatment of titanium alloys leads to the formation of discretely structured regions of residual stresses in the surface layer, which is connected to one of the following factors: the heat source (sinusoid), and on the other hand, the martensitic structure which is discrete. The significant role of the deformational effect on the material when residual stresses formation is shown. In particular, it has been established that in the case of an increasing loading on the tool from 10 N to 250 N, the value of the tensile residual stresses decreases by 3 times.