Metallurgical Metamaterials: A strategy for manipulating shock waves using metallurgy

Existing methods to design metamaterials for dynamic loading involve tuning the crushing behavior so that sufficient energy can be absorbed over extremely short time scales. While this approach is effective for manipulating and dispersing low to moderate amplitude loads, when lattice-based metamaterials are subjected to large-amplitude shocks they are destroyed and lose many of their desirable traits. In this work we utilize volume-changing phase transformations to achieve metastable crushing at the atomic scale, which is reversible, stable to finite-amplitude shocks, occurs on the time scale of 10s of nanoseconds, and can be fabricated using conventional techniques. The phase transformation pressure is readily tuned by modifying the local composition and can be described using the standard solution model. As an example, finite element simulations and shock loading experiments are used to show how to design a metallurgical metamaterial from gradient Fe-xMn laminates that can disrupt, disperse, or amplify shock waves whose magnitude ranges from 5-15 GPa. While Fe-based alloys are promising, an assessment is made of the relative potential of most base elements across the periodic table. Development of this new class of metallurgical metamaterials for high-pressure, transient phenomena appears to address several shortcomings of existing metamaterial design approaches for extreme loading scenarios, but is still in its nascent stages of development.