A Life Prediction Method for Cyclic Plasticity by the Maximization of Mechanical Dissipation

Dissipation represents an irreversible deformation process and is crucial for the fatigue life of materials. A precise calculation of the evolution of dissipation under cyclic external loading can guide prediction for the fatigue life of materials. The corresponding constitutive equations must be thermodynamic consistent. Based on the first and second thermodynamic laws, we derive the constitutive equations of a unified viscoplasticity model by the maximization of mechanical dissipation, where the dissipation rate is theoretically expressed. This enables one to unify the deformation description and life prediction for complex fatigue loadings. The proposed model is compared with a series of experimental data on cyclic plasticity in 42CrMo4, and it shows good agreement with the data. This suggests that the model has promising potential for evaluating the mechanical response and degradation of materials from a thermodynamic perspective.