Uniaxial crushing of constrained tubes

Abstract

By changing the end constraints, the behaviour of mild steel and aluminium alloy tubes of relatively low D/ t ratio, subjected to an axial crushing load, is studied. Many combinations of end constraints were produced by radially constraining one or both ends of the loaded tube outwards, inwards or in both directions. Partially constrained mild steel and aluminium tubes are found to collapse into either a pure concertina mode or a pure diamond mode, depending on the ratio D/ t and the material characteristics. Mixed concertina-diamond modes would generally result by radially constraining the tube at both ends. Constraining the tube radially outwards at one end does not significantly affect the load-displacement characteristics and the mode of collapse. However, constraining the tube radially inwards produces a different mode than that observed under outward, inward or combined outward/inward constraint. New modes of collapse have been observed under different combinations of outward and inward constraints at both ends. Fully constraining the tubes in the radial direction results in the removal of the initial overshoot in the load-displacement curve, which is responsible for the overestimation of the mean crushing load and the energy absorption capacity of tubular elements. The mode of collapse and the energy absorbed could be controlled with the proper choice of the end constraints.