Lateral confinement as a means for enhancing load bearing and energy absorption in axially compressed tubes

The energy absorption and load-bearing capacity of single and concentric multilayer tubes under axial compression are studied with an eye toward optimization per structural mass or volume available for deformation. The specimens are laterally confined on their inner and outer surfaces by rigid walls to stabilize the deformation, but the effect of confinement diminishes as the number of layers is increased. The diameter of the tubes and the tightness of the confinement or relative density ρ are systematically varied. The confinement tends to reduce the wavelength of the characteristic buckle, which leads to additional energy dissipation modes over the classical tube, notably axial compression and friction. Simple analytic relations are developed to assess the mechanical performance as a function of ρ and other system parameters. When considering mean stress, crush energy and stroke or densification strain on the basis of minimizing mass and volume simultaneously, ρ≈0.5 seem to be a viable choice, resulting in considerable enhancement of the performance over common cellular structures, for which ρ is typically <0.1.