Nonplanar shockwaves and complex spall damage morphologies induced in bi-material target plates

Heterogeneous materials and multi-material structures offer unique opportunities to optimize the structural and functional performance of engineered systems. One drawback of such systems is that dissimilar material interfaces are often sources of stress concentrations that can trigger premature damage initiation and complex damage evolution. The main factor driving such stress concentrations is mismatches in thermo-mechanical properties across the dissimilar material interfaces. Under quasi-static loading, the nature of these stress concentrations has been fairly well studied. However, for shock loading, there is a lack of understanding in how wave speed mismatch (WSM) affects interfacial damage nucleation and evolution. Here, we propose a methodology to isolate and systematically study the effects of WSM on damage morphologies in bi-material target plates absent in other sources of stress concentrators. Finite element simulations are conducted with the phases of the bi-material target plates having different mass densities, which introduces the desired WSM. Other than this WSM, the two phases share the same elasto-plastic properties, which are modeled via a Voce-type hardening law and the Gurson–Tvergaard–Needleman damage model. The results reveal a nonplanar shockwave front and a complex damage morphology, both of which are exacerbated with increasing WSM. Interestingly, complex wave interactions lead to an unexpected shielding of the interface, which could potentially be exploited to improve the performance of multi-material structures subject to shock loading.