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Thin-walled structures have been widely used as energy absorbers due to their significant advantages on crashworthiness and light weight. Relatively few studies have been reported about thin-walled structures with variable diameter along the longitudinal direction in a nonlinear manner. In this paper, a new functionally graded thin-walled structure with variable diameter (functionally graded tapered tube, FGTT) is introduced; and its crashworthiness is comprehensively discussed in terms of specific energy absorption (SEA) and initial peak crushing force (IPCF). The results show that FGTT is of great advantages on energy absorption over the conventionally straight/tapered circular tubes under the same weight. Then, a parametric study is carried out to investigate the effects of wall thickness, gradient variations of section and diameter range between top and bottom diameters on the crashworthiness of FGTTs. Finally, the multiobjective non-dominated sorting genetic algorithm (NSGA-II) is used to further optimise the FGTTs for maximising SEA and minimising IPCF. The optimal FGTTs are found to have superior crashworthiness and great potential for energy absorber. [ABSTRACT FROM PUBLISHER]

Thin-walled columns have been widely used in the protective structure due to their excellent energy absorption capacity and lightweight property. The paper proposes a new design method of the sandwich column composed of a double circular column and a core column to enhance the structural crushing performance under the axial crushing load. The quasi-static crushing test is conducted to investigate the collapse process of the AA6061-O aluminum alloy sandwich column. The good agreement between the experimental test and numerical analysis validates the accuracy of the finite element model of the sandwich column. Then, the numerical investigations of the sandwich column and corresponding members are performed under the dynamic impacting load. The results show that the interaction effect of the sandwich column and corresponding members can significantly improve the energy absorption of the sandwich column. Furthermore, the effects of the geometrical characteristics of the sandwich column are further investigated on the crashworthiness. The results show that the peak height A and number N of the peak of the core column have an important influence on the energy absorption and distribution of the collapse mode. Moreover, the sandwich column with A = 4 mm and N = 14 has the greatest energy absorption capacity. In addition, the wall thickness distribution of the sandwich column plays an important role in energy absorption during the crushing process. Therefore, the results of this paper provide a new method to design the thin-walled structures with high energy absorption. Image 1 • A new sandwich column is proposed to improve the energy absorption of the thin-walled structure. • The sandwich column has higher energy absorption that the double circular column and the core column. • The geometrical parameters A and N have significant effect on the crashworthiness of the sandwich column. • The thickness of the core column has larger influence on energy absorption than that of the inner column or outer column. [ABSTRACT FROM AUTHOR]

• A bionic tree-liked fractal method is introduced to design an energy absorber with high crashworthiness. • The theoretical model is developed to predict the energy absorption of the tree-liked fractal structure. • The fractal coefficient and wall thickness have significant effect on energy absorption. • The 3rd order tree-liked fractal structure has higher energy absorption than typical multi-cell structure. A tree-liked fractal method is proposed to develop a novel protective structure with great energy absorption. Triangular, square and pentagonal tree-liked fractal structures are developed, and their mechanical behaviors and deformation processes are conducted by quasi-static axial crushing testing. The theoretical model of the tree-liked fractal structure is introduced to analyze their energy absorption under quasi-static and dynamic loads. Then, the numerical comparative study of the tree-liked fractal structure on crushing characteristics is further carried out based on high accuracy finite element model. The tree-liked fractal structure has great potential to improve specific energy absorption and crash force efficiency compared with the single-walled structure, and the 3rd order tree-liked fractal structure exhibits the best carrying capacity. In addition, the parametric design is adopted to obtain an optimal fractal coefficient and the optimal distribution of the wall thickness of the 3rd order tree-like fractal structure. Furthermore, the crashworthiness comparison of 3rd order tree-like fractal structure and typical multi-cell structures with the same mass is performed to reveal the advantage for the energy absorption. The finding of this study offers an effective design concept for developing the lightweight and efficient energy absorber. [ABSTRACT FROM AUTHOR]

• Mechanical behaviors are experimentally investigated for wood-filled columns. • Wood column with longitudinal grain orientation is better for energy absorption. • Synergistic effect can promote the energy absorption of wood filled columns. • The wood-filled aluminum column has high crushing force efficiency. Composite structures with high crushing characteristics are drawing great attention in the structural design due to their excellent lightweight and high strength. This paper aims to investigate mechanical responses of natural wood columns and wood-filled aluminum or carbon fiber reinforced plastics (CFRP) columns under axial crushing load. Parametric studies are performed on the material of the external wall, the grain orientations (longitudinal, tangential, and radial) and the growth rings' gradient of the wood (Toona Sinensis) by experimental test. Experimental results show that grain orientations of the wood and the material of the external wall have remarkable influences on the collapse mode and the crushing force, and the wood column with longitudinal grain orientation presents the best energy absorption. In addition, the plastic buckling process, collapse mode and crushing force response of wood-filled composite specimens are comprehensively investigated under axial crushing load. It is found that wood-filled aluminum composite columns present progressive collapse mode and higher crushing force level than wood-filled CFRP composite columns. Furthermore, the synergistic behavior between the external wall and wood filler is evaluated. This study offers insights on designing novel energy absorber with high crashworthiness capacity by applying novel wood fiber materials. [ABSTRACT FROM AUTHOR]

• Three corrugated sandwich columns are proposed to improve the energy absorption of the thin-walled structure. • Parameters A and N of the core tube have a significant effect on the mechanical properties of the sandwich column. • The theoretical model of three corrugated sandwich columns are developed to predict the mean crushing force. • The discrete optimization design is performed to obtain the optimal design parameters of the three sandwich columns. The paper proposes a design method of the sandwich column with the corrugated sinusoidal core and develops the triangular corrugated sandwich column (TCSC), quadrangular corrugated sandwich column (QCSC) and hexagonal corrugated sandwich column (HCSC). The experimental tests of the TCSC and QCSC with A = 8 and N = 1 are conducted to estimate the crushing responses and the reliability of the numerical model of the sandwich column. The crushing responses are numerically investigated of the TCSC, QCSC and HCSC with different geometrical characteristics and the same mass under the axial impacting load. The results show that the energy absorption of the sandwich column is significantly affected by the geometric parameters A and N of the sinusoidal core tube, and the sandwich design has the large advantage of the energy absorption over corresponding members. Furthermore, the theoretical model of the mean crushing force is derived using the simplified super folding element theory, and the comparisons on experimental result and the finite element analysis demonstrate high prediction accuracy of the theoretical model. Lastly, a numerical optimization is proposed by combining orthogonal experimental design and discrete optimization to obtain the optimal crashworthiness of the sandwich column. Optimization results show that the discrete optimization method can be fast convergence and obtain the optimal design parameters. The energy absorption of the optimal sandwich column is about 10% higher than the initial design. Furthermore, the HCSC has the highest specific energy absorption under the same mass and design constraints. [ABSTRACT FROM AUTHOR]