Instrumented Card-Gap or SPHF-Plate Test

The deflagration to detonation transition, or DDT, was studied by means of the shock-pass-heat-filter (SPHF) method using Composition B donors in all cases and Composition B, HBX, and Baratol receptors. The SPHF plates were glass, steel, brass, and aluminum. The influence of donor charge diameter and length, and the receptor diameter on the sensitiveness limit, the curves of S1 vs τ′, and S2 vs τ′ were established for these conditions. A striking result is that S2/τ′ proved to be constant equal to the (effectively sonic) velocity of the initial (relatively) unreactive shock wave in the receptor prior to the DDT; it was independent of donor and receptor charge size, the SPHF plate thickness and type. Based on observation with nitromethane, Dithekite, and liquid TNT by the University of Utah and U. S. Naval Ordnance Test Station groups the phenomenon that eventually initiates the DDT forms on the receptor surface of the SPHF plate as a luminous spot that then flashes effecting the DDT at the instant it collides with the (relatively) nonreactive shock front. The present results are entirely consistent with this mechanism, even though one does not observe the flash-across in the opaque solid explosives.