Out-of-plane crashworthiness of bio-inspired hierarchical diamond honeycombs with variable cell wall thickness

Recently, honeycombs with hierarchical structure or variable wall thickness have attracted more and more attention in engineering applications. Inspired by the structure of natural honeycombs, a novel bio-inspired hierarchical diamond honeycomb with variable wall thickness (HDH-VT) is proposed firstly by introducing wall thickness variation into hierarchical diamond honeycomb (HDH), and its mechanical performance and crashworthiness under out-of-plane impact are studied using an experimentally and theoretically validated finite element method. The results show that the deformation of HDH-VT can be classified into three typical modes, and the corresponding deformation mechanism is analyzed. Subsequently, comparisons of regular square honeycomb, HDH and HDH-VT are performed and illustrate that HDH-VT exhibits superior crashworthiness, and the reason for the superiority is analyzed. Moreover, the effects of basic parameters on the crashworthiness of HDH-VT are explored. Finally, theoretical models for the plateau stress of HDH and HDH-VT are derived, and theoretical predictions correspond well with the numerical results of HDH and HDH-VT with stable deformation modes.