Ideal energy-absorbing metamaterials based on self-locking bistable structures

Energy-absorbing materials with high absorption capacity and self-locking mechanisms are ideal candidates for impact protection. Despite great demands, the current designs either have limited energy absorption capacity or lack self-locking capabilities. To address such limits, we propose a novel type of energy-absorbing metamaterial with both a rectangular force-displacement curve for efficient energy absorption and a steady-state transition capability for locking. By combining the curved beam customized through topology optimization with a snap-fit structure, the ideal energy-absorbing structure is achieved. The deliberately engineered locking mechanism, activated after energy absorption, endows the structure with high programmability and the capability for flexible adjustment. Experimental characterization through additive manufacturing confirms that the error between the force-displacement curve of the designed structure and the target is less than 8.55%, and the energy absorption capacity is improved by 75% compared to the unoptimized bistable structure. The locking of the steady state is accomplished sequentially, which ensures the precision and reliability of the design and provides a basis for application in energy absorption systems. Moreover, the metamaterial also exhibits exceptional impact resistance and protective properties, as confirmed through experimental testing. This study rigorously integrates complex nonlinear mechanical behaviors, paving a new way for the development of highly controllable and optimized energy absorption systems.