Impacting metamaterials: The threshold for wave propagation in holey columns

Abstract

We study the dynamic deformation of columns containing a periodic array of holes subject to impact loading. When compressed slowly, holey columns buckle beyond a critical compressive strain, and global pattern switching (from circular holes to orthogonal ellipses) occurs instantaneously. In contrast, the dynamic deformation of holey columns is driven by wave propagation; impact induces a compressive wave that buckles the ligaments surrounding a hole, nucleating a sequential pattern switching process. Subsequent void collapse, which ultimately leads to self-contact and topological modification, is driven by the moving boundary. Here, we identify the critical impact velocity above which the compression can no longer be considered quasistatic, and we show that it depends on system size. For dynamic deformations, we show that internal displacements are independent of impact velocity and propagate at the material sound speed, whereas the topological transition wave propagates at a speed that depends on the impact velocity. Published by the American Physical Society 2024