This paper presents a further investigation into the energy absorbing behaviour of axially splitting and curling square mild steel and aluminium tubes. Both quasi-static and dynamic tests were conducted. A simple quasi-static kinematic model is developed which describes all the main features of the deformation process. It is assumed in this model that cracks start from the four corners and propagate along the axial direction due to continuous fracture/tearing. The free side plates so formed by cracks roll up into four curls with a constant radius. Formulas for the average crush force, curl radius, and the energy absorption are achieved by analysing the 'far-field' and 'near-tip' deformation events and the bending moment at the crack tip. This quasi-static model is also extended and used for dynamic cases to explore strain-rate effects in splitting square metal tubes. Solutions are presented and detailed comparisons are made between theoretical predictions and experimental results.