Sciencemadness Discussion Board

Where the detonation starts?

Turner - 12-12-2013 at 16:10

Hi,

I have been wondering if a given mass of material (say C4) shaped in a ball is detonated with a regular blasting cap which is taped to the side of this material. The detonation would start on the outside of the material instead of starting in the center of the mass and moving out. Would there be any performance differences between these two cases? Even though the general idea for HE is to have the detonator centered in the mass.

If that is the case then I wonder if an EBW spiraled through a cylindrical mass of explosive material (C4) so that there is a lot of contact thru out the volume of material, and this is detonated, the performance of this explosion would be better than if this same amount of material was detonated with an ordinary detonator.

I don't know anything about EBW's but I am assuming that the electricity travels instantaneously through the wire.

Dany - 12-12-2013 at 20:31

Practically no difference in detonation performance (detonation velocity and pressure) in the two case. If a series of detonator (e.g., EBW) are detonated simultaneously around a cylindrical mass of HE a shaping of detonation wave will occur. An implosion type nuclear warhead uses this principle. A spherical mass of high explosives surround the pit or a mass of plutonium 239 (the pit is subcritical). a series of detonator (EBW) are detonated simultaneously to form a convergent detonation wave toward the center of the HE mass where the pit is present. the high pressure detonation wave compresses evenly the spherical pit mass to supercritical. This is not an easy task. the implosion should be very symmetric or the nuclear warhead will dude or detonate with very low yield. the work on explosive lensing of the first atomic bomb was performed by George KISTIAKOWSKY at Los Alamos National Laboratory.

Another application of wave shaping is the FCG or Flux Compressing Generators. A cylindrical mass of HE surrounded by multiple detonator is detonated so as to compress a magnetic flux generated by a permanent magnet or by a helical coil connected to a capacitor bank. These compact generators can generate magnetic fields up to several thousands of Tesla and Millions of amperes in a transient fashion. These generators can be made also by single point implosion (implosion using one detonator). For more info see Explosive Pulsed Power for Larry L. Altgilbers , Jason Baird , Bruce L. Freeman , Christopher S. Lynch , Sergey I. Shkuratov.

If you are a novice in EBW's i suggest you to read Chapter 25 of the book Explosive Engineering (Paul W. COOPER). The Chapter is entirely dedicated to EBW detonators.

Dany.



[Edited on 13-12-2013 by Dany]

DubaiAmateurRocketry - 12-12-2013 at 23:40

If we used a more powerful detonator/booster than the main explosive, will the shock wave travel faster through the explosive's own VoD and therefore explodes in less time frame and generate a higher detonation pressure/velocity ??

Dany - 13-12-2013 at 02:32

@DAR,

If the booster used has higher Dcj and Pcj the detonation wave will start in the main charge with detonation parameter higher than the predicted by the 1-dimensional ideal theory of detonation (or Chapman-Jouguet theory). This is called an overdriven detonation. However, this regime will decay with time (as the detonation wave advance in the explosive) back to the "normal" detonation parameter predicted by the theory (this mean the parameter calculated at the Chapman-Jouguet plane also called the sonic locus, at this locus D=u+c where u is the particle velocity and c is the velocity of the sound in the detonated explosive).

Dany.

Ral123 - 13-12-2013 at 13:48

Do you know what happens if there's an inert layer, like 1-2mm PVC between the booster and the charge. The Grunny velocity will be much slower.
Have you ever wondered if you initiate cast ETN with pure HMTD, when the ETN detonates, will the HMTD be compressed back to less then it's original volume :D ?

Dany - 13-12-2013 at 19:17

Quote: Originally posted by Ral123  
Do you know what happens if there's an inert layer, like 1-2mm PVC between the booster and the charge. The Grunny velocity will be much slower.
Have you ever wondered if you initiate cast ETN with pure HMTD, when the ETN detonates, will the HMTD be compressed back to less then it's original volume


What are you talking about??? Grunny velocity...?????

The configuration that you give (inert layer of PVC at the interface charge/booster) is a well known configuration of the Gap test. However, in the Gap test we use Poly(methyl methacrylate) (PMMA) instead of PVC. The PMMA will serve as an attenuator of the shock wave given by the booster. If you know the unreacted Hugoniot of both PMMA and the explosive charge, you can calculate the pressure induce in the explosive at the inetrface PMMA/charge. So the Gap test is an important tool for diagnostic the shock sensitivity of high explosives. Why we use PMMA? for two important reasons:

1-the material is well characterized (the unreacted Hugoniot is well known)

2-the material is a transparent one, so you can visualize the shock wave as it advance in it and thus you can calculate the velocity of the shock. Knowing the shock velocity, the unreacted Hugoniot and the density of PMMA you can calculate the pressure in any point in the PMMA.

Dany.

Ral123 - 14-12-2013 at 09:00

I guess I should read more books, because I don't get what are you saying.