Rate-dependent combined necking and fracture model for predicting ductile fracture with shell elements at high strain rates

Abstract

This paper introduces a rate-dependent extension of the Hosford-Coulomb ductile fracture initiation model combined with a non-local localized necking criterion (rate-dependent DSSE-HC model) for predicting ductile fracture initiation in metals with shell finite elements at high strain rates. A Johnson-Cook-type hardening model, which consists of strain hardening, rate-sensitivity, and thermal softening terms, was adopted together with an associated flow rule. The temperature was treated as an internal state variable that was calculated from the plastic strain energy using a strain-rate-dependent weighting function between the isothermal and adiabatic conditions. The parameter associated with the localized necking locus for a specific strain rate was obtained using the instantaneous strain hardening rate. The proposed extension of the DSSE-HC model was implemented in a user-defined material subroutine and validated for virtual DP590 notched tension and punch-loaded circular disc specimens by comparing with fine mesh solid element solutions.