Numerical Modeling of Energy Dissipation during Fatigue Crack Propagation in Metals

Abstract

It is well-known that mechanical work spent on inelastic deformation of metal converts into the heat. However, experimental studies have shown that process of plastic deformation is accompanied not only by extensive heat dissipation but also by energy storage. Therefore, precise calculation of the dissipated energy value should take into account the portion of energy which is accumulated in the material. In this work, we applied thermodynamic constitutive theory based on multiple dissipation potentials to obtain constitutive equations for structural parameter responsible for the stored energy and plastic strain causing plastic dissipation. Evolution equation for structural parameter is derived from phenomenological form of free energy function. Combined hardening model is used for plastic strain calculation. Value of the dissipated energy is calculated as difference between plastic work and stored energy. We have applied this model to calculate dependence of dissipated energy per cycle on crack length for two titanium alloys (Ti-5Al-2V and Grade-2). Simulation was carried out in finite-element package Comsol Multiphysics in plane stress formulation. A stationary crack approach was used for energy balance calculation at the crack tip. Results of the simulation were compared with experimental data on heat dissipation obtained by original heat flux sensor.