Relative effectiveness HE filling in British bombs

[Antoon]

As you al know British bombs (and also other nations) had different kind of HE fillings.

Looking for the relative effectiveness of the same bomb with different fillings mostly the TNT-equivalent is used.
I use the following numbers:

TNT = 100% (1)
Amatol 80/20 = 110 % (1.1)
Amatol 60/40 = 91 % (0.91)
Amatol 50/50 = 97 % (0.97)
Pentolite D1 = 133 % (1.33)
RDX/TNT 60/40 = ?
Minol 2 = 120 % (1.2)

I know there is a lot of discussion about TNT-equivalent, but there must be a rule of thumb to compare the effect of the same bombs with a different filling.

Can someone confirm this and/or has additions?

Greetings - Antoon

 

[Dreamk]

Hi Anton!
I worked on this a number of years ago. I'll look in my files but this will take time as they are presently in boxes due to upgrading works in my flat.
Best regards

 

[Eggburt1969]

As you al know British bombs (and also other nations) had different kind of HE fillings.

Looking for the relative effectiveness of the same bomb with different fillings mostly the TNT-equivalent is used.
I use the following numbers:

TNT = 100% (1)
Amatol 80/20 = 110 % (1.1)
Amatol 60/40 = 91 % (0.91)
Amatol 50/50 = 97 % (0.97)
Pentolite D1 = 133 % (1.33)
RDX/TNT 60/40 = ?
Minol 2 = 120 % (1.2)

I know there is a lot of discussion about TNT-equivalent, but there must be a rule of thumb to compare the effect of the same bombs with a different filling.

Can someone confirm this and/or has additions?

Greetings - Antoon

Effectiveness in what parameter... blast peak pressure, blast impulse, fragmentation (metal driving), cratering (mechanical energy transfer), etc.?

 

[FZG76]

Cyclotol or Comp B are :
Comp B 60/40 : 1,16
Cyclotol 70/30 : 1,14
Cyclotol 75/25 : 1,11

 

[Houndsworth]

I am no expert but I did some research for a future public display of equipment used by the SAS (and of course others) in WW2 that will include dummy explosives. It will be next to my replica SAS jeep.

I assume you are talking about the brisance number, which is a quantitative measurement of shattering power, meaning detonation pressure. I think this is the rate where the explosive reaches its maximum detonation velocity, which is the speed of the pressure wave travelling through the explosive. It is calculated based on velocity and density. TNT was so popular it was given a brisance of 1.00 and other explosives are related to that with respect to detonation pressure. If I am not using the correct terms, perhaps an expert will let us know.

I have read that PETN has a brisance of 2.2. This went into Cordtex cord, and when mixed 50% with TNT became Pentolite
RDX was 1.94 by itself. As an aside, with beeswax it was called Composition A . With 39% TNT and 1% beeswax it was Comp B. If 88% RDX and 12% explosive plasticizing oil containing Tetryl and Nitrocellulose it was called Comp C or more commonly, PE No. 2. In the U.S., Comp C evolved over time into C-2, C-3, and C-4
I think Pentolite was 1.26 but you could be right at 1.33
Baratol was well below 1.00 but I don't know the number

 

[Tom]

As you al know British bombs (and also other nations) had different kind of HE fillings.

Looking for the relative effectiveness of the same bomb with different fillings mostly the TNT-equivalent is used.
I use the following numbers:

TNT = 100% (1)
Amatol 80/20 = 110 % (1.1)
Amatol 60/40 = 91 % (0.91)
Amatol 50/50 = 97 % (0.97)
Pentolite D1 = 133 % (1.33)
RDX/TNT 60/40 = ?
Minol 2 = 120 % (1.2)

I know there is a lot of discussion about TNT-equivalent, but there must be a rule of thumb to compare the effect of the same bombs with a different filling.

Can someone confirm this and/or has additions?

Greetings - Antoon

Antoon,
What you are looking for is the "RE Factor" [relevant equivalency]. One way to look at all the different main changes used is to ask, what's the point? The RDX/TNT 60/40 you list provides a good example as it is a standard filler in grenades, mortars and artillery. When testing a mortar [for example] there will be specific fragmentation requirements for certain density at various distances, which ends up calculating into the death and injury distances. After conducting a test, if the frag produced is to big to meet the number and density requirements, they can increase the RDX in the ratio, which is a faster HE and the explosive will produce smaller fragments. In the US, this is called Comp B and can range from an 80/20 to 50/50 mix of RDX/TNT. This way, they can adjust the main charge to meet the requirements without having to design and characterize a new explosive mix.

 

[Bombdoc]

Shell and bomb fillings are arrived at via a number of factors, not just explosive performance..

In wartime availability of strategic components and ease of filling is a significant factor. Some compounds are easy to fill into shells and bombs depending on capacity. Poured fillings tend to suffer from unacceptable shrinkage in large capacity munitions, and although gaps and voids are acceptable in an air dropped munition, they can lead to bore prematures in shell if they collapse on setback. Many of the Amatol mixes were designed to be filled by pressure in a paste form to minimise shrinkage.

During WW2 Germany was critically short of oil based chemicals and resorted to the use of many "strange" bomb fillings to make up the difference. These fillings proved to have short storage lives and continue to present challenges to EOD dealing with recovered examples. In many cases the fillings have undergone significant chemical changes and are typically in a much more sensitive state than when they were dropped. Often the filling poses a greater explosive risk than the fuze train.

Insensitivity is another factor. Semi armour piercing projectile fillings need to be able to withstand severe impact shock without detonating. Picric Acid or Ammonium Picrate was sometimes used for these fillings, known as "Dunnite" or Composition D in the US. SAP has fallen out of use these days and Picric compounds are rarely used.

In some bomb and underwater weapon fillings, aluminium is often added to increase the temperature of the explosion to increase the size and energy of the gas bubble produced. Typical fillings include Torpex and Minol.

Modern explosive fillings are moving to compounds with low sensitivity to improve storage safety and reduce hazards to gun crews etc from ammunition explosions. These "Insensitive Munitions" do not necessarily have lesser performance characteristics however they do present challenges to the fuze designer and add to the difficulty of disposal by demolition.

 

[TimG]

Below might be what you're looking for -

Further to the above - it wasn't just bomb fillings where the Germans used 'strange' fillings. A lot of fillings used for projectiles used all manner of materials to bulk out the explosive. The 'Fp' series of explosives - TNT/Sodium Chloride (table salt) ranged up to 70% salt, that said it still had a velocity of detonation of 5,000 m/sec. I believe Major A.B. Hartley in his book 'Danger UXB' makes mention of dealing with bombs where their fillings had become liquid due to the high level of contaminants and also some that were very gaseous.

TimG

 

[Eggburt1969]

The relative equivalence ratio, in relation to TNT, of an explosive material is normally given by the formula below (see image as I can't paste in formulas).

Where:

Q = energy released (heat of explosion/detonation) per unit mass. i.e. kilojoules per kilogram.
V = volume of gases evolved on explosion/detonation per unit mass, i.e. decimetres cubed (a litre) per kilogram.

In relation that of TNT, i.e. Q (TNT) and V (TNT).

You also have power index, which is essentially the same as above, but in relation to picric acid (trinitrophenol).

The relative equivalence ratio/power index ratios are crude ways to give quick comparisons of explosive materials.

As mentioned above the actual equivalences vary so much between the various parameters, such as blast peak pressure, blast impulse, metal driving and mechanical energy transfer, that the equivalences/indexes aren't all that useful in reality.

 

[Speedy]

As you al know British bombs (and also other nations) had different kind of HE fillings.

Looking for the relative effectiveness of the same bomb with different fillings mostly the TNT-equivalent is used.
I use the following numbers:

TNT = 100% (1)
Amatol 80/20 = 110 % (1.1)
Amatol 60/40 = 91 % (0.91)
Amatol 50/50 = 97 % (0.97)
Pentolite D1 = 133 % (1.33)
RDX/TNT 60/40 = ?
Minol 2 = 120 % (1.2)

I know there is a lot of discussion about TNT-equivalent, but there must be a rule of thumb to compare the effect of the same bombs with a different filling.

Can someone confirm this and/or has additions?

Greetings - Antoon

Hi
Amatol in most common meaning is a mixture of ammonium nitrate (AN) and trinitrotoluene (TNT). Designation index like Amatol 80/20 means that mixture contain 80% of AN and 20% of TNT. As the pure AN is much weaker explosive than TNT, it's very improbable that Amatol 80/20 could be stronger than pure TNT.
Amatol 20/80 could be as strong as pure TNT or even little stronger.
As many people wrote here, there's no universal criteria for measure or calculate such explosive power. But in most cases, you could estimate such "power" from two factors:
- explosive with higher detonation velocity (Vdet) is usually stronger than one with lower Vdet
- explosive that generate more gaseous product of detonation is usually stronger than one generates smaller amount of gases

TNT has much higher Vdet than AN; but generates less gases than AN. So, i think such Amatol like 20/80 or so could be a little stronger than pure TNT. Because the drop of Vdet caused by small amount of AN could be insignificant, but higher volume of gases could make difference.

 

[Tom]

Attached is Appendix D from my book, which [scroll down] includes Russian designations with explosive configuration. The same explosives are used worldwide, but with different names from country to country. Well, except for DNN with is garbage. But it's used extensively by the Chinese in ordnance they export, and by the Russians in their TD explosives [T=TNT, D=DNN, G=RDX]. Also used by other other countries to a lesser extent.