primaries detonation physics

[pdb]

To my knowledge, we have a pretty good idea of the detonation physics in HE, thanks to high-speed frame cameras (video now), sensors of all kinds and the like. But when it comes to primaries, the picture is less neat, as it is quite difficult to explain how a shockwave can occur in very small loads of explosive with a fast DDT (Pb(N3)2, AgONC, DPNA etc). Some authors in the sixties have mentionned a possible "resonance" in the detonation process, but I don't know exactly where we stand today.

Can anyone enligthen me about this fascinating phenomena ? I've been looking through litterature with little sucess, as this research field does not seem to passionate many...

[Cricket]

The way I see it to work is that once the material is ignited, it will continue to deflagrate until the gas made from deflagration provides enough heat, pressure, and confinement around the area to allow for the DDT. I never thought of resonance occurring, but it certainly could I think. And if/when it did/does, I could see it aiding in the DDT process. It's very interesting. If it were a powder, rather than a solid, I would think resonance occurring slower and less efficiently. I would also think that DDT in a material would be affected by things as simple as the manufacturing technique and the temperatures at that time. It would affect crystal size -> surface area -> speed of deflagration -> speed of gas production -> the density of that gas produced -> speed of the pressure produced needed to obtain DDT. And if it were a pressed solid, then things like the texture of the thing that pressed it would also matter in that same way. It would alter the surface area. And the actual flammability and VOD (deflagration, not detonation) of the molecule are probably the biggest factors in the speed of DDT. And things like physical structure would matter (powder, solid, crystal, density of these, ect.). So, it is sort of complicated, but it also makes sense. I don't know if all this shit is correct or not, but it seems logical to me. So until someone tells me the better, I believe this. Later.

[pdb]

I would roughly agree with all the factors you listed, that can impact the DDT characteristics.

However, to come back on the beginning of your post, some experiments have been conducted with metal acetylides (Ag, Cu) exploding in vacuum. They showed that in such conditions (no air around, and no gas generated), mechanical effects are still observed, even on very small quantities... which is quite puzzling !

[a_bab]

I think it is not.

When Ag2C2 explodes, the products are of course Ag and C, in a gaseous state. So even with Ag2C2, you'll get gaseous products. As the explosion products are gases, ejected at high speed/temperature, you'll get a heck of a mechanical effect.

The vacuum means no sound, but that doens't means no mechanical effect.

[pdb]

I am aware of this argument. But I think it's a little short and I stiil believe that detonics experts do not consider the detonation process in tiny loose primaries loads the same way than in an "infinite diameter" cylinder of HE. I had some years ago the opportunity to spend a few months in two detonics labs (one French, one German) and, although this suject was not explicitely addressed during my stay, it was evident that people were looking at the two phenomena differently.

However, it would be nice to read other members' opinion. Again, I never found much litterature about ithis specific subject.

[vulture]

The resonance theory could explain why NG can only undergo low order DDT from flame, because the resonance energy will be severely dissipated by the liquid, which can't happen in the solid state.