Homogenized Modeling of Anisotropic Impact Damage in Rolled AZ31B with Aligned Second-Phase Particles

Magnesium is attractive for ballistic applications due to its high specific strength, but is not widely used due to its lower ductility as compared to other traditionally used materials (e.g. aluminum, titanium, and steel). Additionally, the behavior of magnesium is highly complex and is not well understood due to its HCP crystal structure and significant anisotropy. This work builds on direct numerical simulations (DNS) of rolled AZ31B magnesium with explicitly modeled second-phase particles subject to high strain rate uniaxial tension. The second-phase particles are preferentially aligned along the rolling direction, which induces anisotropies in void nucleation rates and void coalescence as a function of loading orientation. We propose a straightforward approach to account for these damage anisotropies in an anisotropic extension of the Gurson-Tvergaard-Needleman (GTN) homogenized damage model. The resulting anisotropic GTN model is calibrated against the uniaxial tension stress-strain responses predicted from DNS calculations for seven different loading orientations. The calibrated anisotropic GTN model is utilized to probe orientation effects in ballistic simulations. Two ballistic cases are conducted: (i) magnesium plate impacted with a steel sphere and (ii) magnesium plate impacted with a steel plate. The results quantify the degree to which preferential alignment of second-phase particles degrades the ballistic performance along the normal direction. This degradation is significant for a spherical impactor case, but fairly insensitive under plate impact. Consequently, the spall strength of rolled AZ31B is fairly insensitive to particle alignment.