Internally nested self-locked tube system for energy absorption

For energy-absorbing systems constructed by round tubes, boundary constraints and/or inter-tube fasteners are required to prevent splashing of tubes from lateral loadings, which results in extra labor and time costs. To overcome this shortcoming, the self-locked system comprised of dumbbell-shaped tubes was recently proposed, which can prevent the lateral splashing of tubes under impact loadings without any constraints. To improve the energy-absorbing capacity of the self-locked system, the internally nested self-locked system is proposed, of which the basic unit is a dumbbell-shaped tube nested by round tubes inside. The proposed nested self-locked system not only inherits the self-locking effect of dumbbell-shaped tubes, but also significantly improves the energy absorption properties. In order to estimate the energy absorption of the proposed tube, a plastic hinge model is developed based on the analysis of the four-phase deformation process of the tube. Besides, experimental study and FEM simulations are also carried out, and the results agree well with the theoretical prediction. Furthermore, the geometric parameters of inserted round tubes and the stacking arrangement of the proposed nested self-locked systems are investigated, and suggestions on designing an internally nested self-locked energy absorbing system are provided for practical applications.