Strain rate and temperature dependent fracture criteria for isotropic and anisotropic metals

Abstract

The newly proposed isotropic ductile fracture criterion (Khan and Liu, 2012), based on the magnitude of stress vector (MSV), is further developed to include strain rate and temperature dependences. Based on new observed responses during quasi-static and dynamic shear experiments, an exponential term is included to simulate the strain rate effect on ductile fracture of Al2024-T351 alloy. The KHL hardening model type temperature dependent term is also included to correlate with the observed temperature sensitivity of the ductile fracture of Al2024-T351 alloy. These modifications allow the proposed MSV fracture criterion to simulate the ductile fracture of Al2024-T351 alloy over wide ranges of strain rate and temperature.Further, by demonstrating the influence of hydrostatic pressure on the anisotropic ductile fracture behavior of a HCP alloy (Ti–6Al–4V), a new uncoupled anisotropic ductile fracture criterion is proposed. To comprehensively consider the anisotropy and tension compression asymmetry in the Ti–6Al–4V alloy, the modified Hill anisotropic function proposed by Khan et al. (in press), is used to describe the geometry of the anisotropic fracture loci in principal stress space. Moreover, the KHL hardening mode type strain rate and temperature terms, in power-law forms, are adopted in the new anisotropic fracture criterion to correlate the fracture strength of the Ti–6Al–4V alloy over wide ranges of strain rate and temperature. Based on measurements at different strain rates and temperatures, a systematic procedure is listed for the determination of the material constants involved in the proposed anisotropic ductile fracture criterion. Furthermore, a generalized form of the fracture criterion, which can comprehensively simulate quadratic, non-quadratic and intermediate type fracture behaviors, is proposed. Excellent correlation between proposed fracture loci and the corresponding fracture observations is demonstrated.