A series of forty axial impact tests were conducted using a drop hammer rig (V_i < 9 m/s, G = 72 kg) and a gas gun system (V_i ≤ 72 m/s) on aluminium alloy 6061-T6 circular shells having 2R/H = 9.6. The tubes were impacted in the gas gun with three projectiles weighing 0.9 kg, 1.84 kg and 5.45 kg, which when combined with the appropriate initial velocities, give an input energy of 2.5 kJ, approximately. Four principal basic collapse modes were revealed in these dynamic tests, namely: dynamic plastic buckling, axisymmetric progressive buckling, asymmetric progressive buckling and Euler, or global bending with one or two plastic hinges, i.e. mode 1 or mode 2. Dynamic plastic buckling is generally observed in the high-velocity impacts prior to any local buckling. It transpires from these experiments that the inertia properties of the striker have an important effect on the initiation of buckling for high-velocity impacts and that the development of the buckling process for the aluminium alloy tubes is sensitive to the initial velocity and the specimen length. Critical lengths at the transition from progressive to global buckling for low speed impacts (quasi-static test conditions) have been identified experimentally and the threshold velocity for dynamic plastic buckling to occur has also been revealed.
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