On the stress state-based coupled plasticity – Ductile damage model for aluminum alloys considering the influence of high-rate impulsive preload

The purpose of this study is to produce a ductile damage model for 7075-T6 aluminum alloy by correlating the effect of stress - state parameters to the pre-mechanical working exited by an impulsive shock loading. A stress state-based ductile damage model is coupled implicitly with constitutive plasticity framework to anticipate a generalized true fracture locus of the Al-7075-T6. To simulate the constitutive equations, a fully nonlinear finite element procedure is developed to capture the corresponding stress state, hardening, and damage evolutions during the high- velocity impact preload as well as a subsequent progressive static deformation in the tensile tests. The results are calibrated by selected experimental tests representing different stress - states. Also, two conditions are investigated for the stress-strain curves obtained from the uniaxial tests; specimens with the high rate pre-mechanical workings and specimen without pre-mechanical workings. Moreover, by applying two fracture initiation criteria, i.e., the Hosford- Coulomb and Xue models, two types of the fracture locus are predicted for the Al-7075-T6 alloys in terms of the plastic strains and stress - state parameters under the conditions mentioned above. By considering the experimental data, a new evolutionary model of the ductile damage, which is coupled with the J2 plasticity is proposed to relate the initial rate - dependent stress state. By using the fracture criteria, our model may be reliable for a phenomenological scheme of the damage evolution and useful for comparisons with the Xue damage model. Finally, analysis of the fracture surfaces by Scanning Electron Microscope revealed that the fracture surfaces of all samples mainly contained the dimples, which indicates the presence of ductile fracture in all specimens before and after the shock loading.