Modeling Magnetic Field and Strain Driven Phase Transitions and Plasticity in Ferrous Metals

A finite strain continuum theory is advanced for static and dynamic simulations of material response under combined mechanical and magnetic fields. The general thermomechanical theory accounts for nonlinear thermoelasticity, plastic flow from slip and twinning, damage mechanics, and phase transformations. Maxwell's equations are implemented in the Galilean approximation. Effects of electromechanical body forces, Maxwell's stress, and magnetostriction are included, as are forces and heating from electric currents in conductors. Several assumptions are newly introduced to facilitate calculations in the context of finite element methods with explicit dynamics. Of particular interest are ferrous solids whose phase changes and interactions are affected by external magnetic fields. Predictions for compression of pure iron, in comparison with experimental data and prior analytical results, verify suitability of modeling assumptions and numerical methods. Further calculations demonstrate efficacy of the model for reproducing experimental findings on ferrous alloys of the same chemical composition but with two different prior heat treatments, leading to different initial microstructures. For all materials studied, effects of magnetic field on kinetic barriers are discovered to be more influential on phase transitions than magnetic Gibbs free energy differences between phases.