Crashworthiness of bio-inspired multi-stage nested multi-cell structures with foam core

Multi-stage nested multi-cell hollow structures inspired by the macroscopic architecture of wood are char-acterized for their energy absorption in this study. After investigating numerous variations, the three best-performing nested multi-cell architectures are revealed using the modified MULTIMOORA (Multi-Objective Optimization on the basis of a Ratio Analysis plus the full MULTIplicative form) methodology. To investigate the influence of the foam core on the crashworthiness performance, an analysis of foam-filled structures with foam core's various density was also carried out. Decreasing the peak collapsing load and controlling the deformation mechanism express the perfect crashworthy characteristics, indicating the efficiency of the multi-stage structure. The structure deformation demands a higher collapsing load level at the second and third stages due to the connection between foam core and tubes, which shows a high reinforcing effect of the architecture being tested. Structure, foam core, and impact velocity are three main factors enhancing the crashworthiness performance of a structure and controlling its collapsing behaviour. The newly conceived architecture revealed peak collapsing load (PCL) and specific energy absorption (SEA) of foam-filled structures increases in the range of 21%-57% and 4%-20%, respectively, while second collapsing load efficiency increases up to 29% at the highest foam core's density, compared with their counterparts. In addition to the numerical analysis, theoretical models that are in good agreement to predict average crushing load (ACL) are also developed for structures with and without foam