Lightweight recoverable mechanical metamaterials for efficient buffering of continuous multi extreme impacts

When projectiles penetrate multistory buildings, their internal fuze microsystem needs to withstand continuous and multiple strong mechanical impacts. Similar mechanical conditions also exist in automobile collisions and in other industrial scenarios. Therefore, buffer materials with high energy absorption and recoverability are essential to protect the core devices of projectiles from failures in such scenarios. In this study, an ingeniously designed lightweight mechanical metamaterial with a bistable symmetric curved beam structure (BCBS) is proposed for high elastic energy absorption performance and recoverability using a bistable mechanical design. Given its significantly lower structural density than that of the traditional configuration, BCBS can maintain the weight of the buffer using a high-strength TC4 material, which aids practical applications such as fuzes. The optimal parameter design of a BCBS was derived using the bending beam theory. Finite element calculations were used to analyze the performance advantages and mechanism origins of the energy absorption and recoverability of the BCBS compared with those of classical buffer materials and negative- stiffness sandwich bistable structures (NSMSs). Further, the experimental performance under two typical mechanical conditions of a projectile fuze was tested using a project-specialized mechanical impact experimental system. After three consecutive ultra-high energy impacts (energy up to 3800 J per impact), the maximum energy absorption ratio and recoverability of the BCBS were found to be 213.2% and 12.1% higher than those of the NSMSs, respectively. The BCBS maintained energy absorption stability under five consecutive ultra-high acceleration impacts (peak acceleration amplitude = 2500 g), effectively protecting the electromechanical system.