Passage of a Detonation Wave Across the Interface between Two Explosives

摘要

This report is divided into two parts. In the first we consider what happens when a plane detonation wave crosses a plane interface, parallel to that front, between two different explosives. The case of most interest is that in which the first explosive overdrives the second, the pressure and detonation velocity in the second explosive having values higher than normal and the Chapman-Jouguet condition not being satisfied. This is known as the 'carry- over' effect and it would persist indefinitely if the two explosives were infinite in extent, but for charges of finite size it fades away in a distance comparable with charge dimensions. The effect of the finite reaction rate is to produce a zone, of thickness a few millimetres, which the detonation front must traverse before the carry-over effect is fully established. Criteria are given for deciding whether or no carry-over will occur in any particular case, and numerical results are given for a few cases in which it does occur. The most interesting result is that carry-over produces a far greater increase in pressure than in detonation velocity. The second part deals with oblique incidence of the detonation front on the interface. Only steady cases are considered and no essentially new result is obtained. The magnitude of the carry-over effect varies with angle of incidence and disappears for sufficiently large departures from head-on incidence. Two subsidiary results of some interest are derived. The first is that the Chapman-Jouguet condition is not sufficient to ensure a steady detonation velocity if the dominant reaction near the end of the reaction zone is of zero order. If the reaction is of higher order then it is never quite completed and we have to define reaction- zone thickness in a manner analogous to the definition of shock-front thickness. The second is that the intersection of two detonation waves inside an explosive is always regular, no Mach wave being produced.