Numerical modelling of P/M steel bars subjected to fatigue loading using an extended Gurson model

The possibility of modelling experiments conducted on P/M steel bars subjected to strain controlled fatigue loading is investigated. The constitutive relation is an extended Gurson model, using a viscoplastic formulation with plasticity driven damage accumulation supplemented by kinematic as well as isotropic hardening. The total damage is modelled as the sum of void growth and void nucleation. Plasticity driven heat accumulation under adiabatic conditions is furthermore included in the model. The damage accumulation was monitored after choosing a kinematically hardening material model. ate effects were investigated. It was shown that by assuming the reference viscoplastic strain rate to be constant, increases in damage accumulation and temperature per load cycle with decreasing loading frequency is obtained. This unrealistic behaviour was shown to be eliminated by choosing the reference viscoplastic strain rate a function of the first invariant of the rate of deformation tensor.