Thin-walled structures are frequently used as energy absorbers in automotive, railway and aviation industries. This paper deals with the collapse and energy absorption behavior of thin-walled structures under dynamic axial loading Numerical modeling was performed using finite element code LS-DYNA. In order to validate the results of finite element analyses, a square tube was collapsed using universal test machine. This tube was then simulated in LS-DYNA, and the results with those of experiments were compared. There was a good consistency between the numerical and experimental results. The tubes with different cross-sections namely square, hexagonal and octagonal shapes reinforced with inside ribs as well as with different scales (ratio of sectional side length of the inner tube to that of outer tube) 0, 0.25, 0.5, 0.75 and 1 were simulated in LS-DYNA. To determine the suitable cross-section in terms of crashworthiness, multi-criteria decision making method known as Technique of Order Preference by Similarity to Ideal Solution (TOPSIS) was employed. The results demonstrated that the double walled tube with octagonal cross-section possessing the scale between 0.25 and 0.5 had the best crashworthiness behavior. To find the optimum values of scale and wall-thickness, response surface method (RSM) and D-optimal criterion using design of experiments (DOE) were utilized Moreover, the effect of number of inside ribs (4 and 8) on the capability of absorbing energy was also investigated and the octagonal tube with 4 inside ribs was selected as an optimal tube with lower maximum impact force.

Keywords: Collapse behavior, energy absorption, Axial loading, Double walled tubes, multi-objective optimization

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