Brisancy?

[me234]

I wasn't sure if this deserved a whole new thread, so I figured the Water Cooler would be best.
I expect a bit of flaming is going to happen over this. I just got a hunch.
So please don't hold back, I generally find that constructive (?) criticism is useful.

Everywhere I look, people are saying that brisancy is determined by the density and the vod of an explosive. Now I know that so far there has been no difinitive definition of the term, and that there are a million other things that kind of contribute to it, but I'm specifically wondering what else (besides vod and sp. gravity) is responsible. I'm not asking for every little thing, just what the major contributors are.

"The rapidity with which an explosive reaches its peak pressure is a measure of its brisance." From
http://www.brainyencyclopedia.com/encyclopedia/e/ex/explosive_material.html#Power

Does anyone here know how to calculate or otherwise determine this value (short of experimental)

The reason why I started this thread is because I read the following with reference to Methyl Nitrate:
"... and its brisance is about equal to that of nitroglycerine." ('Explosives' Rudolf Meyer 1977)
And while this might not seem strange, the quote was found in the same book as the following figures:
for NG:
'Detonation Velocity 7600m/s
Density 1.594g/cc
Heat of Explosion 6322kJ/Kg'

for Myrol
'Detonation Velocity 6300m/s
Density 1.217g/cc
Heat of Explosion 6121kJ/Kg'

Taken from 'Explosives' by Rudolf Meyer 1977
A book I have found highly informative and feel is trustworthy.

So if brisance is primarily a function of density and vod, how does one account for the fact that myrol has almost the same brisance that NG possesses?
I included the heats of explosion because they seemed to be the only values that were close enough together when looking for functions of explosives that might contribute to the brisance.

So please, if anyone can provide me with any clues as to what other factors might explain brisancy, I would be most grateful.

[hereno]

VOD is only relative to its containment/volume and initiation. You will find a whole range of VOD figures for the two explosives you have mentioned, both of which are able to detonate at high and low velocity. Methyl nitrate is capable of >8000m/s if its hit hard enough while in a large enough column.

Anyway, "brisance" cant be calculated as such, its a relative term. You could try calculate energy release, gas volume and VOD but you wont know anything until its tested. For example silver acetylide is said to have simular brisance to its double salt with AgNO3, but the double salt has better oxygen balance, higher VOD and a superior initiator (referenced from Fedoroff). Give reason to that!

[me234]

You see, that's exactly what I'm talking about. I would love to know the why's behind it.
I'm beginning to wonder if the reasons don't end up going down to bonding level at all. Or maybe even decomposition mechanisms?

Dammit, this kind of topic is going to lose me my mind one day.

[nbk2000]

Real world testing is the order of the day, as 'brisance' isn't something that can be reliably modeled yet (AFAIK).

If you can, you could cast blocks of concrete with holes in them, and place small charges of equal weight of various explosives into the holes, and compare the fracture radius created by each explosive.

The more 'brisant', the larger the fracture zone. :)

[Rosco Bodine]

Think of "brisance" as the "ability for shattering" a target material ,
not stretching , tearing , or bending it but actually granulating the
target into the smallest pieces .

Brisance is a characteristic related to the "quickness" of the particular explosive ,
regarding the time duration required for energy to be released .
A brisant explosive releases all of its energy in a very brief interval ,
which creates a sharp rise in the kinetic energy delivered by the
supersonic pressure wave impacting the target .

Brisant explosives deliver energy to the target at a rate which so
far exceeds the elastic deformation capacity of steel , that the metal
actually shatters like breaking glass , into splinters , flakes , and
sharp edged particles which are broken along the crystalline lines .
The number of the fragments is directly proportional to the brisance
and the size and mass of the fragments is inversely proportional
to the brisance .

[FrankRizzo]

It also most likely has to do with the resonance and wave propagation in the material being tested upon. If you think of sound waves, low frequency sound energy will pass through much more material without loss versus the same energy at a high frequency (electricity being the opposite). Resonances that occur when the bonds of the explosive material are being broken probably play a big part in its efficacy.

[tmp]

Rosco Bodine, I'll go along with you on the definition of brisance, that
is the "shattering" effect. Many years ago that term was used to
describe the effect of ANFOs. ANFOs could be modified, usually through
granulation and charge density to either shatter concrete or break soft
coal into large lumps - all using the same weight of charge. It does seem
that higher density of the charge and higher VOD produces more brisance.

[me234]

I must agree with TMP, Rosco's definition does make a lot of sense.
It also goes with what I got from Brainyencyclopedia (see earlier post).
And Brainyencyclopedia must be right: when looking up other stuff along these lines, they have Mega's site as a place to go see for further information.
I thought that was cool.

The time 'till peak pressure definition might also be able to account for why Tim whatshisname claims AP to be a brisant explosive.

dammit, what is his last name? Oh well.

Now I know that marble isn't the most malleable of substances, but I have 'allegedly' witnessed ~50-75g APPN (with a touch of Al) reduce a ~10x20x30cm Block of marble to, well, nothing. Couldn't find a damned particle bigger than run-of-the-mill dust off your floor. I was suitably impressed. Please note, the charge could have been a bigger bigger/smaller. I didn't actually weight the charge.

As always
Thanks for the input

[meselfs]

Just a little note: besides VOD and density, the gases produced matter also, very much in fact.

Take note that one mole of any gas (provided it has a very low boiling point) occupies around 22.4 mole. With that in mind, nitrogen producing explosives work well, which partially explains why most monopropellants are nitrogen based.

[K9]

Just a little note: besides VOD and density, the gases produced matter also, very much in fact.

Take note that one mole of any gas (provided it has a very low boiling point) occupies around 22.4 mole. With that in mind, nitrogen producing explosives work well, which partially explains why most monopropellants are nitrogen based.

I think you meant 22.4 litres ;)

[FUTI]

I think that the nitrogen is involved in so many explosives because it can form nitro groups and make good oxygen balance, and on combustion (explosion) it makes stable nitrogen molecules releasing some more heat for other gases to expand...but then again I had nothing to back this up...just guessing...AFAIK at the moment of explosion water produced in it is also in the gaseous state, so there is no nitrogen advantage over it.

[Rosco Bodine]

A steel target plate , or even aluminum or lead is a better indicator
of brisance than a target material of brittle material like rock or coal
or concrete . The cutting ability of an explosive is also directly related
to brisance . Even explosives that are mildly brisant like AP will
reduce a brittle target material to dust . But you could do the same
with one solid blow of a sledgehammer . The relative difference
in brisance is more readily observed on targets which are preserved
mostly intact after the test , so that the relative distortion or
the number of pieces can be quantified and compared for different
test charges on the same standard target . AP and some other
mildly brisant explosives are curious in a way that they can make
more noise and actually sound more powerful than the work they
do on a target material would indicate . The physical evidence
is the true measure of the brisance , and what level of brisance
is best is a subjective mater for the application . For example
if chunk coal is your desired result , you wouldn't use the same
type of explosive as would be best for cutting structural steel .
The choice of explosive that is best for a particular task depends
greatly on what is the nature of that task . Different explosive
compositions are highly optimized for a specific application .

[me234]

Rosco, I realise that Marble is brittle and therefore not ANYwhere near a suitable brisancy test medium. I just added the comment 'cause I thought it was kinda cool.

I always thought that nitrogen was common in explosives because it bonded endothermically to oxygen, one of the better oxidising elements. Thus it gave it up exothermically, helping to provide some of the energy require to break carbon - hydrogen bonds etc., and then to oxidise these elements. That's why I think that peroxides are generally explosive, the O - O bond breaks easily, freeing up oxygen for further reaction with the reducible elements in the compound.

If I'm wrong, I would REALLY like to know it. Going through life ignorant is a terrible thing.

[meselfs]

I always thought that nitrogen was common in explosives because it bonded endothermically to oxygen, one of the better oxidising elements. Thus it gave it up exothermically, helping to provide some of the energy require to break carbon - hydrogen bonds etc., and then to oxidise these elements. That's why I think that peroxides are generally explosive, the O - O bond breaks easily, freeing up oxygen for further reaction with the reducible elements in the compound.

If I'm wrong, I would REALLY like to know it. Going through life ignorant is a terrible thing.

True, that's the other half of the story :)

[Pb1]

Take note that one mole of any gas (provided it has a very low boiling point) occupies around 22.4 mole.

That's only true at STP. For other conditions the combined gas law is used. It goes: P1V1/T1 = P2V2/T2, where T is in K.

[me234]

The 'till-peak-pressure definition makes sense to me because I can just 'see' a charge of explosive being suddenly converted to a large no. of moles of gas that occupy the relatively small volume of the charge and then propagating outwards, driven by the pressure gradient.
So a more brisant explosive will produce its total amount of gas in a shorter period of time, not allowing much gas to be driven away before the rest of the explosive is converted to gas, thus increasing the overall pressure gradient at the time when all of the explosive has been consumed. Thus the gases will move faster, with a higher pressure, with a greater shattering and shearing effect.
So, if this is right, and it's somewhat dependant on pressure gradients, would a given explosive be more brisant at higher altitudes? I know, I know, when you're dealing with millions of Pascals, a fraction of an atmosphere doesn't make much difference, but I was just thinking of the age old adage "every little bit helps".
This might also help explain why brisancy is density and vod dependant:
vod: the faster the propagation of the wave through the explosive medium, the faster the explosive solid -> gas conversion takes place, same argument as above.
Density: 1-when all the gases are produced they occupy a smaller initial volume.
2-helps with vod.

One might also argue that velocity of wave propagation away from detonating substance is related to brisancy, or more correctly, to 'The rapidity with which an explosive reaches its peak pressure', rather than the brisancy being dependant on the vod.
Or maybe they're not necessarily consequences of each other, maybe they're independent phenomena that seem related.

Shit, I think I'm starting to go around in circles. I need a break.
Any thoughts and insights into the above circles is very much welcomed.

[ProdigyChild]

Excellent me234, I like your ideas! I perfectly agree.

I also searched for a reason, why

Brisancy = VOD*energy output

should not hold. I came up with 2 mechanisms that allow to violate this formula (all theorie of course, I'm not spreading knowledge here!). This overlaps with your thoughts:

a) the shattering of a explosive could be done in steps and the first step is already sufficient to propagate detonation.
Myrol is much simpler than NG - this would back this theory. Also Silver acetylide vs. double salt.

b) complex gas molecules have different energy storage possibilities (1-atom can only move in 3 dimensions, 2-atom can additionally rotate 2-dim, 3-atom molecules laking all rotation symmetry, plus all the possibilities of swinging. Rotation and swinging in my opinion is undesirable, because this energy is not DIRECTLY available as pressure withing the very short time of start of detonation. Storing energy wastes brisancy. I really wonder, if energy is balanced between movement and rotation at the first microsecond of expansion.
So explosives which produce more N2,O2,CO2 and less H2O should be more powerful. AP is expecially bad, because of large reaction molecules.

However, Myrol produces more H2O than NG - pity for my theory. But that's when mechanism a) dominates ;)

[FUTI]

to me234 and ProdigyChild: You guys had stated few things that make the little ringing sound inside my head:) But I will listen the Chinese who said "it is not wise the one that said many wise things, but the one that kept it's stupid ideas for himself", so I won't say anything until I check the idea that has crossed my mind. It will take a few days...

[Boomer]

Just my two cent:

The old definition of brisance ("Brisanz nach Kast") was in fact VoD x energy output, with the latter being per volume. The formula is brisance = VoD x specific energy x density. If you check the units you get watts per square cm, meaning it is the power density of the det front(m/s x J/kg x kg/m^3 = j/s/m^3 = w/m^3).

The newer theory sees the pressure as a measure of brisance, but the detonation pressure, not the pressure of the expanding gasses like Me234 and Prodigy suggested. Det pressure is 200-300 tons per cm^2 while the hot gasses after the shock wave have 10-15 tons. The latter would not pulverize metal, only bend/tear it (-> difference LE pipe bomb - HE grenade).

Det pressure is proportional to VoD^2 x density. Because VoD is roughly proportional to density for a given HE, brisance is proportional to density^3 !!! That is why every effort is made to pack the shit only a little bit tighter by special pressing/casting methods.

[me234]

Sorry if I seem a bit obsessed with the pressure shit, I just got stuck on the visual of a piece of soft steel undergoing elastic / plastic deformation with a slow (" 'till peak pressure") explosive, and then the same metal being shattered with a faster (above definition) explosive because it doesn't have the time to under go deformation before it reaches fracture point.

And yes Boomer, I get what you're saying with the 'detonation pressure' rather than the gasses after det has gone to completion. But I'm having difficultly 'seeing' what causes the pressure DURING detonation. If it's something stupid and simple that I've overlooked, please just call me an idiot and then tell where I went wrong, thanks.

ProdigyChild, could you elaborate on your step-wise shattering ideas, they sound interesting.

Futi, I know that we haven't done anything particularly exciting here, but I AM the not-wise-one, that's why I came here with this topic, I want to be educated. So please, once you have completed what you feel to be necessary to validate your theories, let us know what they were and how they turned out, even if they didn't work. I would still enjoy reading about them. A negative result can often be just as useful as a positive one.
So anyway, I wish you luck with whatever it is you're doing.

[Boomer]

I had the same problem until I thought "what IS a det front?".

Just imagine the molekules (aka plasma) smashing into the target at 20 mach. Don't be fooled by thinking "but it is only gas" : at 2000000 PSI there is no difference between gas, liquid and solid - they are all the same density (actually above that of the explosive btw).

In a nutshell:

1/2 pound C-4 detonated on ony surface = 1/2 pound hammer hitting that same surface at 20 mach.