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In this paper, the energy absorption parameters are investigated for new forms of thin-walled energy absorbers. The effect of adding stiffeners to the outer tube wall, as well as the multi-cell effect of the structure, was investigated both in a separate and simultaneous manner in a tube with the square section. This design has not been investigated in previous studies, and it stimulates innovation in its own right. Such designs can significantly increase the energy absorption of the structure with the least change in the initial geometry and the lowest costs. The nonlinear explicit finite element method was used to simulate the crushing process in the tubes. The numerical simulation results were validated with the results of experimental tests, and a good agreement was observed. Finally, the parameters such as specific energy absorption, crush force efficiency, initial peak force, and mean crush force were calculated and analyzed. The results showed that the proper combination of stiffeners in the middle sides of the tube wall and the creation of a multi-cell column made it possible to improve the specific energy absorption up to 89% and crush force efficiency up to 52% compared with the reference tube, which is a significant improvement. Also, while comparing some of the results, it was analyzed why sometimes inserting stiffeners on the outer wall of tubes is better than the multi-cell method to increase the SEA of structure.

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Thin-walled structures with nested cross-sections have been introduced in recent years as structures with high energy absorption capacity. In this research, a new type of energy absorbers is introduced, which is a combination of two different elements which are subjected to lateral and axial loads simultaneously. The study has been done experimentally and numerically; in the numerical part, LS-DYNA software was used for computer simulations. The outer part of the introduced absorbers has square shells with a thickness of two millimeters that absorbs energy under lateral loading. The inner part of new absorbers is a shell with a rectangular cross-section that collapses under axial compression. The obtained results showed that these structures can increase the energy absorption by 36 and 32% of the total energy absorbed through each component separately. In the experimental part, the accuracy of numerical results was checked, and good agreement was observed. In the final part of this research, using Minitab software and based on the response surface method (RSM), the most optimal absorbers in terms of specific energy and maximum force were introduced.