Experimental study on the impact resistance of fill-enhanced mechanical metamaterials

Mechanical metamaterials are attracting increasing interest as artificial architected/composite materials with unprecedented physical properties and promising engineering applications. To address the gaps in current research, particularly the lack of comprehensive insights into reusable, adaptive behaviors and the potential for enhanced energy absorption in the zero Poisson's ratio (ZPR) domain, a family of 3D ZPR mechanical metamaterials composed of thin-plate and axisymmetric thin-shell segments is introduced. Mechanical performance, self-recovery under large deformations, reusable, and strain rate-dependent adaptive energy absorption are achieved. Furthermore, the mechanical performance and functionality of the semi-closed structure composed of both plates and curved shell (SPCS) are further enhanced by filling shear thickening gel (STG). Quasi-static compression and drop-weight impact tests are carried out to investigate the mechanical properties of the SPCS and the influence of impact velocities on its energy absorption performance, quantifying the enhancement effect of filling STG and demonstrating the resistance of SPCS to secondary and even multiple impacts. The extrusions resulting from spatial constraints between the axisymmetric shell containers and the STG fillers enhance strength and plateau stress, improve impact resistance, and enable adaptive energy absorption. The variation in stiffness and energy absorption of filled-SPCS with strain rate adeptly resolves the conflict between comfort and functionality in designs such as wearable protective devices, blast protection, and reactive armor, thereby paving the way for the development of strain rate-dependent mechanical metamaterials. Collectively, a series of ZPR mechanical metamaterials, which offer better energy absorption, broader applicability, enhanced adaptability, and reusability compared to traditional lattices, are introduced. This contributes to insights and guidance to the development of cushioning energy-absorbing metamaterial designs.