Shock to detonation

Explosive substances can also be detonated if they are subjected to a high velocity shockwave this method is often used for the 

---

In these tests NMe showed the detonation-to-shock and shock-to-detonation transition characteristic of a homogeneous expl even with barriers as thin as 25fi- The reaction zone had a peak of probably less than 1 Ofi thickness. Nonporous 60/40-RDX/TNT was less sensitive to disturbance by thin barriers than NMe. A 250/r thick barrier could cause a disturbance in the reaction, but there was no delay and very little overshoot of the type usually associated with homogeneous expls. Experimental arrangements shown in Figs 1, 2, 3, 4 and 6 are not reproduced here... 

Jacobs et al, "The Shock-to-Detonation Transition in Solid Explosives , 9thSymp-Combstn(1963), pp 517-29 11) G.E. 

Accdg to Price (Ref 15), in studying shock-to-detonation transitions a frequent question is whether a certain expl is extremely insensitive to shock or is, in fact, nondetonable under the test conditions. To answer it, some investigation must be made of the critical diam (dc) of cylindrical chges, i.e., that diam above which, deton propagates and below which deton fails. The loading density rather than the diam can be varied in that case, the critical density (pc) is detd. Pairs of such values form the detonability limit curve which divides the d—vs—p plane into one region where deton can occur and another where it must fail. 

Similar records have been obtained for PBX 9404 (Refs 37 65) and RDX and HNS (Ref 20a). All these records show that shock-induced decompn begins near the shock entry face forming a compression wave that eventually overtakes the input shock and effects shock-to-detonation transition... 

In these latter studies, strong shockwaves were produced by driving the free edge of the molecular solid with a steadily moving piston as depicted in the lower part of Fig. 3. Two-dimensional simulations were initially carried out to determine the piston driven shock-to-detonation threshold in the perfect crystal. Once this threshold was determined, a crack such as that depicted at the top of Fig. 19 was introduced. Additional simulations were then performed for a series of piston velocities near, but below, the critical piston velocity, Vp, that is necessary to cause detonation in defect-free... 

For strong shockwaves the presence of a single crack such as that depicted in Fig. 19 (top) was found to significantly reduce the shock-to-detonation threshold. This is demonstrated in Fig. 19 (bottom). This figure depicts the shockfront position versus time for a series of simulations... 

The results demonstrate that nanometer wide cracks can have severe effects on the shock-to-detonation threshold. It might be tempting to conclude that the chemical reactions caused by these defects result from a velocity doubling as atoms are spalled into the crack. Indeed, we found that the velocities of the leading particles that are spalled into the crack by the shockwave had approximately twice the particle flow velocity in the shockwave, as predicted by the continuum theory. However, we also observed that when these high velocity molecules struck the opposite side of the crack, reactions were not induced immediately. Rather, the complex motions of the many atoms within the crack appears to seed the chemical reactions that ultimately cause detonation. These studies lay the foundation for additional studies with more complex models. 

We summarize a number of simulations aimed at deciphering some of the basic effects which arise from the interaction of chemical kinetics and fluid dynamics in the ignition and propagation of detonations in gas phase materials. The studies presented have used one- and two-dimensional numerical models which couple a description of the fluid dynamics to descriptions of the detailed chemical kinetics and physical diffusion processes. We briefly describe, in order of complexity, a) chemical-acoustic coupling, b) hot spot formation, ignition and the shock-to-detonation transition, c) kinetic factors in detonation cell sizes, and d) flame acceleration and the transition to turbulence. 

Hot Spots, Reactive Centers, and the Shock-to-Detonation Transition... 

Secondary explosives, those that do not easily go from deflagration to detonation, do not initiate electrostatically with ease, and require larger shocks to detonate. They include nitrocellulose, PETN, and desensitized nitroglycerine. 

J. H. M. Fu and G. E. Cort, Numerical Calculation of Shock-to-Detonation from Projectile Impact , Los Alamos Scientific Laboratory report LA-8816-MS (1981). 

---