Propagation of reactive cracks and characterization of reaction violence in spherical charge under strong confinement

High temperature gaseous products of conductive burning on explosive surface can penetrate into preformed crack inside explosive bulk under high pressure to form so-called convective burning. The high rising gaseous products pressure resulting from the convective burning in turn will create cracks inside the explosive bulk, leading to the formation of new channels for convective reaction and the more reaction surfaces for burning. In this paper, a new experimental method is designed for a pressed HMX-based PBX, in which a highly confined spherical charge is ignited on center point via non-shock initiation. The propagation of such kind of reactive cracks inside is recorded and evaluated with the total reaction violence growth behavior characterized by reaction pressure and confinement wall velocity profile. In the experiment with a transparent window, the early stage evolution of crack inside explosive sphere is invisible and the crack system after the crack break through to the spherical surface shows a 4 fold symmetric crack pattern which is deduced to be related with outer layer confinement conjunction manner. The violence evolution experiences a sustaining low pressure growing rate stage for 100 μs. Then it is observed that a rapid burst pressure in about 10 μs is up to over 1 GPa during the confinement wall movement stage, which gives to a typical explosion outcome with ～20% of bare explosive detonation calculated by air blast over pressure. In the experiment with a 20 mm steel wall, the velocity of the wall has reached 500 m/s at the moment of confinement wall rupture.