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

•Chiral metamaterial with much higher impact-mitigation efficiency is proposed for mitigating repetitive impacts.•Experimental results show that the impact-mitigation efficiency per unit mass can reach over 5 times higher than that of similar materials known by authors, with much fewer cells and much higher stiffness.•Extra energy dissipated by torsion caused by compression-torsion coupling effect is the key factor for superior mitigation performance.•Compression-torsion coupling effect widens the bandgap to low-frequency and prevents more waves pass through.•Gradient design is proposed to cope with large impact loads with improving mitigation efficiency. 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.