An internally nested circular-elliptical tube system for energy absorption

The force-displacement curve of circular tubes under lateral crushing load is typically divided into three stages. However, the plateau force actually shows a linearly increasing trend under compression load. As a matter of fact, a stable plateau force is remarkably important for the energy absorption devices. In an effort to overcome this drawback, this paper proposes an internally nested energy absorption system consisting of a circular tube and an elliptical tube, and it is promising to replace the single circular tube as the dominated impact protective structure in the helicopter seats. The experimental investigations of the circular tubes, the elliptical tubes and the nested circular-elliptical tube system (CETS) are carried out to study the mechanical behaviors of the tubes subjected to the lateral crushing load. In addition, an analytical model for the CETS is established on the basis of the rigid-perfectly plastic material model. The results indicate that the plateau force of the circular-elliptical tube system is extremely stable while the single circular or elliptical tubes has the plateau forces linearly increasing or decreasing. Besides, the 3D finite element model of the nested tube system is developed through LS-DYNA, and it is also validated by comparison with the experimental result of the CETS. Based on the numerical simulations, a parametric investigation is conducted to understand the effect of the internal radius of the circular tube, the ovality of the elliptical tube, the number of elliptical tube and the impact velocity on the mechanical response and crashworthiness characteristics for the CETS.