This paper deals with the crashworthiness capability of newly designed bitubal columns with different polygonal cross-sections (i.e. triangular, square, hexagonal, octagonal, decagonal and circular) reinforced with several inside ribs. A large number of finite element analyses were performed on these columns under axial and oblique impact loads using LS-DYNA to find the crashworthiness indicators. These columns were studied with five different size ratios (the ratios of the perimeter a of the inner tube to the perimeter b of the outer tube), namely a/b = 0, 0.25, 0.5, 0.75 and 1. A decision-making method, which in this case is the technique for ordering preferences by similarity to the ideal solution, was then employed to select the better columns which possessed a higher energy absorption and a lower peak force. The bitubal columns with size ratios a/b of 0.5, 0.25 and 0.75 were generally found to be the best cases. Furthermore, the multi-cell columns with the decagonal and octagonal cross-sectional shapes were selected as the best energy absorbers.

Auxetic structures, with re-entrant (inverted hexagonal or bow tie) unit cells, have received considerable interest due to their negative Poisson’s ratio property that results in superior mechanical properties. This study proposes a simple method to create non-homogeneous re-entrant honeycombs by modifying the size of chevron crosslinks. The various structural designs were conceived by changing the geometrical dimensions of the crosslinks, namely the length ($l_{cl}$) and the thickness ($t_{cl}$), while maintaining the parameters of the re-entrant cell walls. The influence of the design parameters of chevron crosslinks on the mechanical behaviour of additively manufactured re-entrant honeycombs was investigated experimentally and numerically. The structures were fabricated using the Fused Deposition Modelling (FDM) technique from polylactic acid (PLA) plastic. In-plane quasi-static compression tests were conducted to extract the elastic, plastic, and densification properties of the structures. Furthermore, a Finite Element (FE) model was developed via LS-DYNA R11.0 software, validated experimentally, and was then used to obtain a deeper insight into the deformation behaviour and auxetic performance of various designs. The obtained results revealed that the mechanical performance of re-entrant honeycombs can only be tuned by controlling the geometrical configuration of chevron crosslinks.

This study aims to investigate the effects of the draw beads on the crashworthiness of the aluminum tubes under axial quasi-static loading. Based on this design philosophy, a total of 12 beading tube designs with various configurations were developed. Within each design, the effect of arrangement bead form on the crashworthiness performance was also analyzed. A finite element model, validated using experimental tests, was used to study the crashworthiness performance and progressive deformation of the tubes. Based on the results, a multi-criteria decision-making method known as Technique of Order Preference by Similarity to Ideal Solution was employed to determine the most suitable tube that features high energy absorption and low impact force. The best tube with a high score was selected to investigate the effect of bead formed direction on aluminum tubes. Consequently, the study identified a bead shape tubes configuration that exhibits superior crashworthiness and low impact force. The beading tube design methodology presented in this study allows the exploitation of variable shapes geometries for the development of high-efficiency energy-absorbing structures and their crushing behaviors.