Topological Protected Mismatch of Mechanical Metamateirals

Recent advances in mechanical metamaterials and topological phases have given rise to topological mechanical metamaterials (TMMs) that exhibit exotic topological properties, thus enabling promising applications such as energy absorption, impact mitigation devices, and stress-avoiding implants. Maxwell lattices, a representative class of TMMs, exhibit attractive mechanical properties at the surfaces/interfaces and distinct properties between different surfaces when they are topologically polarized. Understanding the motions and deformations of the topological Maxwell lattices is critical for designing impact resistant metamaterials for mechanical and biomedical applications. However, most studies on dynamics of TMMs focus on the linear regime and rarely take the topological effects into account. To address this knowledge gap, molecular dynamics simulations using the spring-mass system are employed to study the dynamics of the Maxwell lattices. Importantly, auxiliary springs are added on the Maxwell lattices to achieve local bistability, and to improve the impact mitigation effects of the lattices. Energy dissipation due to friction is also simulated through introducing a damping term. Various impact loadings and boundary conditions of the lattice (with/without bistable units) are studied to compare the reaction forces transmitted from the impact surface to the opposite edge and kinematic characteristics. The theoretical analysis is employed to identify how the topological polarization causes different impact resistance at different surfaces. The new findings can improve the design of topological Maxwell lattice that can exhibit high-performance impact mitigation and energy absorption properties and can enable the applications of TMMs in architected scaffolds for cell and tissue engineering, engineered bioimplants, and meta-implants for minimally invasive delivery.