Monday, 1 December 2014

HE vs. Armour

I've briefly explored the effect of high explosive ammunition on armour (disappointing American HE and much more exciting Soviet HE of various calibers), but nothing exceptionally scientific. However, a paper by V.V. Gayun, A.V. Grishkun, O.P. Gusev, and A.V. Lisin titled Investigation of Damage Dealt by High Exposive Fragmentation Shells to Armour published in the Armoured Journal (Bronetankoviy Vestnik) gives some glimpse into how shells of various calibers act against armour. In the interest of brevity and not getting bogged down in scientific jargon, I will only translate a portion of the article and provide some figures.

Thankfully, there is plenty of practical data to go off here, and not just theory. The experiments involved 152 mm shells, whose devastating effects we have already seen, as well as Soviet 100 mm, 115 mm, 125 mm, and 130 mm shells. Of course, only knowing where you stand is of limited use if you cannot compare your progress with that of the potential enemy, so the British 120 mm gun with its HESH shells also makes and appearance. These shells are fired at armoured plates 2700 by 2500 by 170 mm, with sensors behind them to measure the impulse, which is judged by the scientists to be proportional to the damage caused inside the tank to its crew and equipment.

Since we've seen what a 152 mm HE shell can do, let's take a look at experimental data for this caliber first. Players of World of Tanks will be used to HE doing the same amount of damage to the tank no matter at what speed its hits, but in reality, this is not the case:

"An analysis of natural shots, static detonations, and calculations shows that the contribution of the explosive filler of a 100-152 mm HE shell contributes around 5-10% of the overall impulse (at an impact velocity of more than 700 m/s), and the main damage to the armour plate is dealt by the impact of fragments.
...
When increasing the impact velocity starting from 600 m/s, the impulse of a 152 mm HE shell grows considerably, and when decreasing it from 400 m/s to 250 m/s, it decreases by 2-4 times. When the impact velocity is 950 m/s, the impulse is 50 and 40 kNs for 0 degrees and 60 degrees respectively, which is 2-2.5 times greater than the 125 mm OF-19 shell.

At angles of impact close to zero, and the velocity of 250 m/s, the impulse of a 152 mm HE shell is less than that of a 100 mm HE shell with the velocity of 900 m/s. When the angle of the target is increased from 0 to 60 degrees, the impulse of shells hitting it at 850+ m/s decreases, but the impulse of shells hitting it at 250-700 m/s increases. Therefore, the 152 mm HE shell has a higher effect against armour than a 100-130 mm HE shell at impact velocities greater than 650 m/s and a comparable effect at lower velocities."

Fig 1. Experimental dependence of the impulse of 152 mm HE shells on the impact velocity (vc) at several angles of impact (α).

The ML-20. whose devastating effects on armour we've already seen. is not a very high velocity gun. Shells hitting the enemy would be flying at less than 600 m/s, giving us a pretty small range of impulse that causes such damage. How does this compare to other HE shells in the Soviet arsenal?

Fig. 2. Experimental dependence on impact angle α of the impulse from HE shells on an armoured plate.
1. 152 mm HE shell (vc = 950 m/s)
2. 130 mm HE shell (vc = 910 m/s)
3. 125 mm HE shell (vc = 780 m/s)
4. 115 mm HE shell (vc = 850 m/s)
5. 100 mm HE shell (vc = 790 m/s)

The 130 and 152 mm heavy artillery is the undisputed king here, but at very high velocities. Corps level artillery and tank guns would be unable to fire shells so fast. 100-125 mm tank guns (the D-10T and its post-war smoothbore cousins) seem like they woudn't do as much damage as we've seen the ML-20 dish out, but comparing the impulse values of these guns to the values in fig. 1 says otherwise. These guns achieve an impulse of about 20 kNs, same as the ML-20.

Now, let's see how these guns compare to British HESH. Unlike traditional HE, the explosive filler spreads itself around the plate it impacts to increase the effect. How much does this increase the effect? Here is the impulse achieved when hitting "a tank" (the specific type of tank is not mentioned).

Caliber, mm Type Impact velocity, m/s Impulse, kNs
Turret
115 OF-18 680 8
125 OF-19 850 11
120 HESH 620 12.5
152 OF-29 800 15
Hull roof
115 OF-18 800 8
125 OF-19 850 9
152 OF-29 800 19
Upper front hull plate
115 OF-18 860 11
125 OF-19 850 14
120 HESH 620 12
152 OF-29 800 28

Turns out, not much better. 120 mm HESH is comparable to the slightly faster flying 125 mm HE, and it still greatly surpassed by 152 mm HE.

14 comments:

  1. The approach doesnt make much sense imo. First of it is explained that the Impuls is greatly depending on the shells velocity. Than HESH is compared to HE on a much lower velocity making the results, according to fig1 (nonlinear dependency, makes linear interpolation useless as well), not compareable.

    From an enginneering aspect however it is visible that HESH creates an impulse about 1,5x higher than that of soviet HE. That is a good result actually.

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  2. >Than HESH is compared to HE on a much lower velocity making the results

    If 620m/s is the speed of the HESH round coming out from the British L11 120mm, then it makes sense. They are comparing the weapons as complete projectile-gun complexes.

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  3. For the l11 its 670m/s according to Wikipedia.
    The 152mm gun was not a tank gun - why is it then listed here?

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    1. Not a tank, but the USSR had high velocity 152 mm guns on self propelled mounts:
      http://en.wikipedia.org/wiki/SU-152_%22Taran%22
      https://ru.wikipedia.org/wiki/СУ-152П

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    2. Both were not mass produced, so it still doesnt make sense imo.

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    3. It's important to evaluate a prospective weapon before putting it into mass production.

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    4. For a mass produced gun that throws the OF29, there's the very famous 2S5 (muzzle velocity 945m/s). Though that's a open-mounted SPG, the Soviets have a penchant of using things for direct fire. (BTW, the 2S3 SPH fires the OF45 ... a different projectile).

      The chart does provide some insight as to why the Soviets never got around to making a HESH round - after reading a table like this, neither would you :-)

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    5. This conclusion is a bit too easy, consider that:
      >>These shells are fired at armoured plates 2700 by 2500 by 170 mm, with sensors behind them to measure the impulse, which is judged by the scientists to be proportional to the damage caused inside the tank to its crew and equipment.<<
      I guess the British didnt come to the very same conclusion. This is a vague guess as it stands there, Do You have more info EE on how the Soviets came to this conclusion?

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    6. There is nothing in the paper about that, sadly.

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    7. That table doesn't tell the whole story. The 152mm would have a V of 800m/s at ~1750m. But would have a V of less that 700m/s at ~3000m. The 120mm would still have an impulse of 12.5 vs turret at that range.
      -m

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  4. Its not a practical way to measure the effectiveness of HE on armor by impulse, what way HE working on armor is also important, HESH is flattened on armor and then detonated, and the paper did not tell anythimg about the possible different itmay make. Also, a RPG would has fewest impulse but must be most effective against 170mm armor, again, the way HE fillings working on armors is i'portant

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    1. If I understand the paper's conclusion properly, the "impulse" is not only the shell's impact, but includes the chemical action of the explosive. Overall, the HESH shells do have an advantage all else being equal, but not as much as people would expect because the contribution of the explosive is only 5-10 percent at typical impact velocities. Even assuming the HESH round's more efficient use of the chemical action increases its contribution by a factor of a few times still makes it only 20-40 percent of the total, not enough to be decisive and perhaps enough to argue a better antiarmor effect can be achieved by flinging a simple HE shell faster.

      It is not clear whether the RPG would have the least impulse because the HEAT jet is hypersonic (much faster than any shell listed here). You are right though in that it would have been interesting to see how these numbers compare to the impulse of HEAT, and also AP and APDS / APFSDS rounds.

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    2. Very interesting thanks for posting :)

      Do you have anything on Soviet research on Fragments vs armour?

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