Investigation of the Process of Deflagration-to-Detonation Transition (DDT) in Granular Secondary Explosives with High-Speed Photography.

摘要

The deflagration-to-detonation transition (DDT) in confined charges of granular secondary explosives has been investigated with high-speed photography. Specially designed steel confinements, which incorporate slit windows to allow streak photography, were constructed to house pressed pentaerythritol tetranitrate (PETN) charges of known density. The results indicate that convective burning is only important during the initial stages of the DDTprocess in causing rapid pressure build-up, and does not govern the deflagration process up to the point of DDT. Following convection, the propagation of the combustion front was found to be governed by the compaction wave generation of hot-spot ignition sites, The transition to detonation is finally attained when the front of a plug of highly compacted material, essentially a second compaction waveformed at the combustion front, overtakes the first compaction wave and causes shock initiation of the uncompacted, and therefore. more highly shock sensitive, original-density PETN. The detonation then propagates to the end of the charge at constant velocity and a rearward shock propagates upstream through the highly compacted plug material and intersects the combustion front. The proposed mechanism is supported by the observed deformation of the internal surface of the steel confinement.