Wednesday, 25 March 2015

Beyond Armour Effects

I previously showed that 50 mm APCR did little damage to the components and crew of a Valentine tank after penetration. But how does APCR perform in general? B.M. Bakshinov, S.V. Lomov, and V.I. Timokhin decided to try it out.

"The main cause of damage when penetrating armour is a stream of fragments. The subcaliber armour piercing shell generates the most fragments, and its parameters are used to determine performance of crew protection measures. However, it is not enough to determine the damage caused by homogeneous steel subcaliber ammunition, since modern foreign subcaliber shells use casings from heavier metals (tungsten, nickel, iron, etc).

An experiment was carried out to determine behind-armour effect of the domestic equivalent. A "sieve" type target made up of two aluminium plates 3 mm each and a steel plate 8-10 mm thick was placed 0.5-1 meter behind 70-220 mm of medium hardness steel. The angle of obliquity was set to 60 degrees from normal, velocity was set to match a range of 2 kilometers. The number of fragments that penetrated the sieve was recorded, as well as their spread from the central axis.

The experiment allowed the formulation of conclusions on behind-armour effect of subcaliber shells:
  1. Two groups of fragments are generated, differing vastly in penetrating power and number.
  2. As excess penetration grows, the number of lethal fragments increases sharply, and then stabilizes.
  3. The angle of dispersion weakly correlates with excess penetration.
  4. There is a limited number of fragments capable of penetrating 30 mm of aluminium at a small spread. As excess penetration grows, their spread decreases.
  5. Most fragments cannot penetrate more than 20-25 mm of aluminium."
Fig 1. Parameters of behind-armour effect of a heavy alloy subcaliber shell. Number of lethal fragments vs: a) their angle of spread, b) in proportion to excess penetration, d) angle of aluminium penetrating fragments and d) penetration of aluminium. Empty shapes are data points, dark shapes and lines are interpolations.

Fig. 2. Fragment spread with 180 mm of excess penetration. The penetration of the fragment is proportional to the length of the cone that represents its group, to scale.

A comparison is also made with effectiveness of domestic shells.


Shell
Fragments capable of penetrating 3-6 mm of aluminium
Fragments capable of penetrating at least 30 mm of aluminium
Number
Angle of spread
Number
Angle of spread
With excess penetration of 100-200 mm
Heavy alloy
200-300
100
7
20-30
3BM9
200-300
100-120
2-3
20-30
3BM15
150-200
110
2
20
With excess penetration of 250-300 mm
Heavy alloy
300-400
100
20-25
12
3BM22
200-300
100
20
24
3BM26
200-300
120
37
32

The article also gives some details on the shell compositions. 3BM9 has an all steel case, 3BM15 has a front heavy alloy core, and 3BM22 and 3BM26 have a heavy alloy core in the rear. The paper reveals that in the latter cases, the fins of the shell and core fragment after they enter the armour, creating more lethal fragments and resulting in a larger angle of spread.

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