High-efficient and reusable impact mitigation metamaterial based on compression-torsion coupling mechanism

Lightweight and reusable materials are desired in engineering for mitigating repetitive impacts. However, the limitation of mitigation efficiency is always a problem in spite of various materials have been studied. And other issues need to be improved, such as bulky and poor load-bearing. There still exists challenge to design a reusable impact mitigation material with high efficient, lightweight and high stiffness. Here, a lightweight syndiotactic chiral metamaterial (SCM) with compression-torsion coupling effect (CTCE) is proposed and fabricated for repetitive impact mitigation. Impact experiments indicate that the proposed metamaterials exhibit significant superiorities in impact mitigation efficiency, lightweight, higher stiffness and less cells over the previously reported ones. In order to reveal the deeper mechanism of the superior properties, the band gaps of SCM with CTCE and isometric chiral metamaterial (ICM) without CTCE are analyzed and compared by transmissibility tests and numerical simulations. It is found that the extra energy dissipated by torsion caused by CTCE is the key factor for excellent mitigation performance, which enlarges the band gap to low-frequencies and prevents more waves pass through. To balance the mitigation performance and load carrying capacity, the gradient design strategy is proposed to cope with large impact loads with maintaining high mitigation efficiency, which is achieved by overlapping the band gaps of different cells to widen the band gap range. The mechanism of improving impact mitigation performance by CTCE revealed in the present work enlightens a new avenue to develop effective, reusable and lightweight buffer materials.