"power" of different explosives??

[Efraim_barkbit]

I was looking through the forum and in some thread I saw something about the difference between VoD and gas volume, and that explosives with a high VoD not have to be more powerful than one with a low VoD, because of differences in volume of produced gas.

so to know the power of a explosive, just knowing the VoD doesn´t mean that much. am I right?
so I was wondering if there has been any tests or studies of the volume of the gas released from explosives commonly discussed here.?(AP,ANFO...)
or might it even be possible to calculate it? (I myself isn´t that deep into chemistry... yet)
it´s like the VoD, nice to know,but it´s not like it really matters when out blasting the shit out of some old treestump...:D

(english is´nt my native language, so forgive me if the grammar or somthing is bad)

[vulture]

Well, this is not an easy question to answer, as there are many factors involved.
Firstly, it is very important that we define the environment factors we are working with, because pressure and temperature have an enormous effect on gas volume.

Normally, gas volume of explosives is listed at 0C and 101.3kPa (1 atm)
A few examples:
TNT:......730L/Kg..6900m/s
NG:.......780L/Kg..7600m/s
HMX:.....920L/Kg..9100m/s
RDX:.....920L/Kg..8750m/s
DEGDN:.1030L/Kg..6600m/s

As you can see, there is no direct connection between gas volume and VoD.
This is logical, as the gas volume is dependant of the chemical composition and thermodynamic properties of the explosive, whereas VoD is mostly dependant of the speed of sound, the reaction speed and the density.

Calculation at a given pressure is possible when making certain assumptions, but this involves physics of which I won't go into detail.

Another variable in the power is the explosion heat.
I will add them to the previous table, together with the oxygen balance:
TNT:......730L/Kg....6900m/s...4520Kj/Kg...-73,9%
NG:........780L/Kg....7600m/s...6770Kj/Kg...+3,5%
HMX:......920L/Kg....9100m/s...5680Kj/Kg...-21,6%
RDX:......920L/Kg....8750m/s...5720Kj/Kg...-21,6%
DEGDN:.1030L/Kg....6600m/s...4530Kj/Kg...-40,8%

We can clearly see that there again is no direct connection between explosion heat and the other variables, however there is a clear connection between OB and explosion heat.
This is agian logical, as a more positive OB means more oxidation and oxidation is where most of the liberated energy comes from.

The brisance of an explosive also depens on the peak pressure at the time of explosion.

Last but not least there is the Berthelot equation which gives you the relative strength to TNT in %.
In fact it is a way to calculate the work (physical definition of work) capacity of an explosive.
The formula:

(840 * N * E)/Mr²

where:
N = # moles of gas produced
E = explosion heat
Mr = molecular weight

Calculation for RDX gives: 194,76%

[Anthony]

First of all, this should be in High Explosives.

Secondly:

"it´s like the VoD, nice to know,but it´s not like it really matters when out blasting the shit out of some old treestump..."

Actually it matters quite a lot. The stump needs to be heaved out of the ground in one piece. Get it wrong and the stump can split into two or more sections, each firmly rooted down - a more difficult challenge to remove than the original stump. Choice how brisant the charge should be would also be dependant on the type of wood, the size of the stump, and its condition e.g. green, rotten, matured.

Vulture has covered the important points quite nicely.

[jfk]

That was quite educational, Vulture.

But since this is a thread about the "power" of explosives, I was just wondering about the different kind of explosive forces that different explosives have. I've heard about "heaving" force and "shattering" force so far, how some explosives explode with a "heaving" force which will move a large body of something in one piece, until of course it comes down out of the sky. Where "shattering" force would result in the complete desolation of an object, i am likening this to AP/HTMD inside a potato (would i be right?)

im looking for an esplosive with a great heaving power, as according to a web site that basicaly said what I've said above, but ive lost the link.

Is there any thruth to this?

[xyz]

Generally speaking, explosives with a low VoD have a lot of heaving power, and explosives with a high VoD have a lot of shattering power. If you are looking for heaving power, try ANFO or Urea Nitrate.

[rooster]

I dont know if the potato think will work so well. If you put ANFO inside it, and was able to detonate such a small amount, i believe it would still be blown to pieces. Maybe by setting the charge on the side of the potato you could see the difference better.

Shattering power, does that mean the power of the shockwave? That the shockwave shatters the object? Or does the heat have something to do with it?

[Microtek]

Brisance or shattering power is mostly a function of detonation pressure which is related to VOD. In my opinion, these parameters give the most useful basis of comparison between explosives ( for my purposes which deal with small amounts of high perfomance HE ).
As a rule of thumb, you might say that work product is important when the charge is buried or otherwise contained completely, while brisance is more important when the charge is placed on the surface of a target.

[green beret]

Dont know if this helps, but in the industry, they have weight strength and bulk strength, I'll find the charts tomorrow, I also have powder factors for stump blasting with ANFO, if I can find it all, I'll post it for you. Also when using something with a high VoD, the gasses tend to escape between the fissures and cracks before the material can be moved any great distance, generally speaking this is with rock but is also applicable to other things, thats why ANFO heaves, because the gasses dont escape too quickly, (in most cases). Sorry if this dosent make too much sense I am tired and just wanted to help a little. It also has to do with the shockwave etc. but I just wanted to say that, it is one of a number of factors which contributes to heave.

Thankyou.:)

[rooster]

Thank you vey much for useful info guys!

Originally posted by Microtek
Brisance or shattering power is mostly a function of detonation pressure which is related to VOD.

Mikrotek, does this mean that the greater VOD the greater pressure? It seems logical that when the wave tracels this fast a certain pressure would build up. But won't the gasses produced in the combustion raise the pressure on surrounding objects? It is calculated in PSI right?

[xyz]

There is also a difference between the pressure that an explosive CAN create, and the pressure that it DOES create. Explosives with a high VoD tend to create high pressures because lots of gasses are formed very quickly.

Because of this, ANFO (which has quite a low VoD) doesn't usually create as much pressure as something like RDX, because ANFO releases it's gasses over a longer period of time and the gasses have more time to escape. But, ANFO has a higher gas volume and CAN create a higher pressure, so long as there is sufficient confinement to stop the gasses from escaping.

Imagine that there were two containers made from a (ficticious) tremendously strong material that could take pressures of a few million psi. Imagine that one contained 1Kg of RDX and the other contained 1Kg of ANFO, the containers are completely sealed. If the explosives inside each one were set off, the comnainers would not burst (because of their enormous imaginary strength) and you would now have two containers that both held ridiculous pressures. The ANFO container would hold a higher pressure than the RDX one because of ANFO's huge gas volume.

[jfk]

thanks all, i guess i was looking for ANFO then. my 25 Kg of 99% grade AN will araive tommorow, im going to do my own experiments on how to remove the hill in my back yard....

[rooster]

Thanx for XYZ, nice way of illustrating that.


JFK: are you able to get any pics of the demolition?:rolleyes:

[Efraim_barkbit]

Thanks everybody for the info, it got me a clear picture of what the meaning of the two definitions of "power" is.

I saw a theory conserning the power increase for explosives some time ago, and I´m wondering if it´s correct.

When X gram of an explosive has power Y, then 2*X gram of the explosive has the power Y^2.

(I hope you understand what I meant, it took some time to figure out how to tell it in english)


were is the part "Rogue science specific"?? is it just gone temporarily, or for ever??

[xyz]

You mean for example, if 1g of AP has a power of X, then 2g of AP has a power of X times X?

[Arthis]

By detonating larger amounts of explosives, you increase efficiency because this creates more pressure in the center of your HE. This means that the total efficiency of twice of amount of HE is greater than twice the efficiency of one.

But I greetly doubt this leads to an exponential law like you said. Imagine that it would mean that 1kg of HE would be far more effective than a pound (X^2 with you notation)... Then 1 ton of PETN would be hiroshima ;) (power of exponentials, used to say my maths teacher...)

[kinetic]

vulture,

i'm not being critical, but curious... where did you get your VoD for RDX?
I have the US Army demolitions manual and it states that the VoD of RDX is 8350 m/s with a relative brisance of 1.60 (TNT being 1.0). I have used these values to determine minimum safe distances and the amount of explosives needed for various charges and I have made and had good results using the info from the manual. This indicates to me that the manual is accurate.

What is the mol. wt. of RDX? Maybe the reason your brisance calculation is different from the manuals is because your VoD is different (obviuosly). So what I am gettting at is I would like to calculate it myself and see. Do you have the mol. wt. of any other explosives?

another reason may be that your system of brisance measurement is not based on TNT.

THanks! :)

[cutefix]

The detonation velocity as listed by Vulture is probably based on maximum density and calculated as some by computer programs in estimating detonation velocity and detonation pressure.
Besides there are many ways to calculate detonation speed and other explosive performance datas and the values vary.
IIRC, in one of the Los Alamos explosive performance data shows RDX to have a measured detonation velocity or 8600 m/s.And in some related explosive data (byPopulato et al?) have its velocity varies according to the density of the explosive.
.

[Cyclonite]

Kinetic, I use 1.75 for RDX. The Army manuals you have used may be extreamly old. I use EOD publications. That may explain something, or it may be that EOD errors on the side of safety, I dont know.

[kinetic]

Actually, the manuals I use are current- I'm still in the army. Every year I go to a seminar where we update the breaching guide (demo manual) and experiment with different charges.

I have done a little extra reasearch since I posted last and I found that different tests and theoretical calculations come up with different RE values even though they are all tested with the same sample of explosive at the same density. I suppose the RE value of an explosive is more of an average or general guideline than a constant...

[vulture]

What is the mol. wt. of RDX? Maybe the reason your brisance calculation is different from the manuals is because your VoD is different (obviuosly). So what I am gettting at is I would like to calculate it myself and see. Do you have the mol. wt. of any other explosives?

another reason may be that your system of brisance measurement is not based on TNT.


You are mixing up different things.

My calculation for RDX calculates the physical work capacity of an explosive, not the brisance. The calculation does not use the VoD, so I don't understand where you're getting at. :confused:
Furthermore the Berthelot equation DOES measure based on TNT.

The VoD comes from a recent (2001) chemical dictionary. I can check the density if you want. Another reason might be that military grade RDX might not be chemically pure, whereas most chemically oriented test use atleast 99,9% grade material.

Furthermore, like HMX, RDX has several crystal modifications which have a rather large impact on VoD.

EDIT: Mr of RDX: 222,6 (off the top of my head)

[kinetic]

Vulture,

AHHHHhhhhh... I see, my mistake- I must have been speed reading or sometihing, you did say that it is in relavence to TNT in the previous thread. :rolleyes:

In the military we use "Relative Effectivenes" to convert pounds of TNT to C-4 or Comp. B in our calculations. RE is a measure of brisance not power (physical work capacity??). That's probably where I got confused. I am curious about this "physical work capacity" though.

Since PWC does not take into account VoD, how can it take into account the detonation pressures? Wouldn't that effect how much matter an explosive can move? Is there any equation or measurement that takes into account all the properties of explosives?

I meant to ask about the mol. wt. of RDX as a separate question but I think faster than I type.

Finaly, where do you find equations like the Berthelot equation? I have looked around and have found very few. I have several in my breaching guide but they mostly pertain to how much explosives it takes to do *blank* rather than the performance/chemical reaction side of things.

Thanks. :)

[vulture]

Physical work capacity could be regarded as the "energy" of an explosive. Power = energy/time and that is where the VoD comes into play, since it determines how fast the reaction proceeds.

The berthelot equation gives you an idea how far 2 explosives would propel an object if they would have the same VoD.