Evaluation of the axial crashworthiness of thin-walled structures with various and combined cross sections

This paper is categorized in three consequent steps to increase the crashworthiness of thin-walled structures subject to dynamic compression in the axial direction. In the first step, a numerical analysis obtains the advantage of each tube with a different cross-section to extract the most crashworthy thin-walled structure. Second, an appropriate combined cross section is designed, and it demonstrates a significant improvement in the crashworthiness (EA, F_mean, F_max, CFE and CS) of the structure. The designed structure is a combination of a square crash box to work at the first time steps of a collision to dramatically decrease F_max. For the rest of steps, a circular crosssection is used to maximize EA and F_mean, and decrease CS. This idea helps to control and enhance the crashworthiness of the structure. Thirdly, a thorough research is done to obtain the optimum length for each one of combined sections. The CFE of the structure increased by 15 % compared to the square section, and 78 % compared to the circular section in spite of decreasing CS. The numerical result of the square cross tube is compared with the existing analytical solution as a sample. Furthermore, numerical results for other cross sections show similar trends to the literature. These two facts indicate the validity of the obtained numerical results.