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Quick question regarding armor


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50+30 in reality is weaker, about as effective as 70mm of homogeneous plate. But in CM, 50+30 is stronger, more like 90mm or more, and regularly bounces 85mm AP at 600m and 76mm down to point blank range. A key component of the notorious "uberStuG", the least accurate bit of armor modeling in CM.

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  • 2 months later...

JasonC,

Wouldn't spaced armor tend to put differential, potentially breakup or deflagration inducing loads on a penetrating projectile, not to mention greatly degrading penetration performance against the primary armor array, thanks to nose erosion upon impact with the face hardened add-on array? The Germans adopted a sandwiched armor shield on the Pak 40 specifically in order to defeat the PTRS- and PTRD-fired Russian antitank rifle projectiles. This is not to say, though, that the Russians haven't gotten a raw deal in terminal ballistics modeling in CMBB.

Regards,

John Kettler

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Spaced and layered are not the same thing. But the first reason they doubled gun shields was just to double the thickness. Single layer has trouble with rifle or MG bullets, let alone an ATR. I doubt very much that an ATR round had any serious trouble with even a doubled gun shield, which is still under a cm of armor. They readily penetrate 3 times that.

The reason two plates are less effective than one is simply that the physical integrity of the thinner overlying plate is vastly less than it would be as additional thickness of integral plate. The overlying plate tends to shatter, especially thin layers.

The naval equations everybody and his brother used to model armor plate vs. projectile since the late 19th century put the effectiveness of 2 plates at approximately the thicker of the two plus about 70% of the thickness of the thinner.

There is a reason the Germans went to integral plate every time, on the next model of vehicle. 30 + 30 became 50mm, 30+50 became 80mm. Of course the extra plate helps compared to not having it (thinner armor), but not compared to having the same weight in a single piece.

Also, face hardening can give all of the benefits of an overlying layer with softer metal behind, without two sandwiched plates.

Modern sandwiching of armors is only done with composite materials, and the point of it is not layering as such, but different forms of strength to handle different forms of attack. (Thus ceramic layers dissipate energy through a wider area when they shatter, and also have the specific heat to defeat HEAT streams; DU layers have the density to defeat dense tungsten or DU penetrators but are too ductile for the face plates on either side, etc).

The operational effects of the real armor series were as follows. German armor type, threat, result.

Early 30-37mm unimproved - Russian 45mm effective, ATRs effective at close range.

30+30mm - Russian 76mm effective, 45mm and ATR ineffective.

50mm - Russian 76mm effective, 45mm and ATR ineffective.

20+50mm - Russian 76mm effective at medium but not at long range, others ineffective.

30+50mm - Russian 76mm still effective at medium range.

80mm - Russian 76mm effective at 500m only, 85mm effective at any range

100-110mm (Tiger hull and Panther mantlet e.g.) - 76mm ineffective at any range, 85mm only effective at 500mm (or a bit longer), long 122mm effective at most combat ranges.

80mm sloped (Panther glacis) - Russian 122mm only occasionally effective (flaws).

The effect of CM overmodeling of layers is to promote the performance of 20+50mm Panzer IIIs to levels actually achieved only by 80mm integral plate. Since they get that on turrets too, this makes the 1942 model IIIs defensively tougher than the 1943 IVs.

Second and most importantly, it makes the 30+50mm StuGs as effective as the Tiger front was historically. Since they cost half as much, this is the single most broken thing in the game and was instantly discovered and exploited by players. (This is made worse by not modeling the 50mm snout area of the StuG, while modeling that of the Pz IV).

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To understand why 50+30 is much weaker than 80mm:

You have to imagine how every atom in the alloy interacts with it's neighbors. The whole point about the mechanical sturdiness of an alloy (or any solid matter) is how the atoms (or molecules) hold on to each other.

Imagine that a pure 30mm plate is being hit head on by an AP projectile and let's say that it penetrates into the metal, making a hole (as opposed to cracking the plate, which I'll discuss later).

The projectile makes a hole by moving the atoms about the center of the impact point to the side. Inside the plate each atom holds on to the one next to it, but also to the one under it (or behind from the projectile's view).

Now, imagine what happens when you are almost through the plate. Then the atoms moving out of the way are only held by the ones next to it, but there are none under it. So the last layers of metal move more easily.

That's the key why 30+50 sucks compared to 80.

In a 30+50mm setup there is this weak point at the end of the 30mm. The projectile can move the last layers of the 30mm plate out of the way without the first layers of the 50mm plate holding on to them.

If you have a solid 80mm plate then every layer has more layers below it that help to hold the atoms in place, and in the 30+50mm setup you have cut through the mutual support.

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Long time since I did solid-state physics, but generally speaking these sort of simple observations are reasonable (this particular one is not, see below) only in ideal-cloud-cuckoo-physics world where all horses are spheres. In reality, things are always much more complicated.

In any case, back in the land of make-believe, you only have to think about this for a short time to see that:

</font>

  • Atoms are less than 1nm across so there are going to be millions of 'layers' in either 80mm or 30+50mm plate.</font>
  • The range of EM interaction between the 'layers' is unlikely (in the extreme!) to extend beyond 100 inter-layer separations (less than 10 seems much more reasonable).</font>
  • This means the projectile has to penetrate, say, ten thousand of what you seem to regard as "hard" parts of the material, and either two or four of the "soft" parts.</font>
  • It is unreasonable to assume that the difference between two and four "soft" penetrations is not going to be swamped by ten thousand "hard" penetrations. (Even if "hard" takes one unit of penetrativeness, and "soft" takes zero - i.e. the maximum possible effect - the difference is only that between 100,000 and 99,998.)</font>
  • There is other physics occurring here. JasonC mentions shattering effects above.</font>

PS. Manufacturing tolerances are going to add thousands of extra 'layers' of hard stuff in different places which would also swamp these edge effects. In this case, we would expect to see more variation across the 80mm plate than between 80mm and 30+50mm. AFAIK these variations are not seen.

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