Abstract: The expansion fracture process and intrinsic physical mechanism of metal cylinder driven by detonation are researched for calculating the initial velocity of fragments. In the experiments, 50SiMnVB steel and 45 steel cylindrical shells with different thickness were driven by TNT explosive detonation. The image information of expansion and the history of velocity were obtained by using a high-speed framing camera and the arrayed photonic Doppler velocimetry. Experiments reveal that the oscillation of expansion velocity is due to shock wave loading, and the expansion velocities of metal cylindrical shells continue to increase after shell rupture. The experimental results show that, for the shells with the same density, the oscillation amplitudes and pulsation times of expansion velocities of the shells increase with the increase in thickness，and the rupture mode changes from pure shear to tension-shear mixing. Because of the different load coefficients caused by different thicknesses of shells, the rupture time of 45 steel shell is later than that of 50SiMnVB steel shell, and with the increase in shell thickness, the difference between rupture time and rupture radius is larger. However, due to the acceleration of detonation products after rupture, the final expansion states of the two steel shells with the same wall thickness are almost the same. Key

Key words: non-standardcylindercharge, detonationdriving, expansionvelocity, shockwaveloading, shellrupture