Thermodynamic format and heat generation of isotropic hardening plasticity

Heat generation due to plastic deformation of metals and steel is studied. Whereas in many investigations it is assumed that the fraction eta of the plastic work transformed into heat is constant throughout the deformation process, the fraction eta is here derived from thermodynamic considerations in a large-strain setting. It is shown that for elasto-plasticity the fraction eta follows as a result of the choice of free energy, potential function and yield function. Taking the stress-strain response and the dissipative properties of the material as basis for calibration, it is shown that the thermodynamic framework of a thermoplastic material is non-unique for the general situation of non-associated plasticity. In the investigation conducted here, the mechanical response and the portion of the plastic work converted into heat (or into stored energy) during plastic deformations is predicted by means of isotropic hardening von Mises plasticity. It is shown that for a situation in which the internal variable is taken as the effective plastic, close fitting to experimental data requires a non-associated format of the evolution law for the internal variable.