Resistance of Layered Plates on PzKpfw IV

[rexford]

Miles Krogfus sent me a U.S. firing test report which indicates that 37mm, 57mm and 75mm APCBC will all fail against the 30mm/50mm frontal armor on PzKpfw IV at 25 degrees side (horizontal) angle. The shots were taken against the strongest armor on the front of the tank at 0, 30 and 45 degrees, and the 25 degree penetration range was interpolated according to the report.

A 25 degree side angle works out to a compound angle of 28.4 degrees from armor perpendicular against the front lower hull (nose), and 26.8 degrees against the driver plate.

Interpolating between the curves in TM9-1907 for face-hardened penetration at point blank:

37mm APCBC fired at 2900 fps

61mm at 28.4 degrees and 62mm at 26.8 degrees

57mm APCBC fired at 2700 fps

81mm at 28.4 degrees and 83mm at 26.8 degrees

75mm APCBC fired at 2030 fps

81mm at 28.4 degrees and 85mm at 26.8 degrees

The report states that 75mm APCBC fired from the M4 aircraft gun could penetrate the PzKpfw IV frontal armor. TM9-1907 shows a 2380 fps muzzle velocity for 75mm M61 fired from an aircraft, with a point blank penetration of 98mm FHA at 28.6 degrees.

The above data suggests that 30mm/50mm layered face-hardened armor resists like a single FHA plate of 81mm+ thickness. While two rolled homogeneous plates in contact resist like a single RHA plate of less total thickness, the U.S. firing results appear to support the British test results against PzKpfw IIIH frontal armor: two FHA plates in contact resist with a single plate thickness greater than the combined two plate thickness.

Paul Lakowski has theorized on the Yahoo! Tankers site that two Face-hardened plates in contact may contain an air space between the surfaces, which could radically decrease the projectile performance. It is also possible that layered Face-hardened plates present a greater effective thickness of face-hardened surface armor to be defeated.

This issue is far from resolved, since the American analysis of penetration ranges was based on the highest limit velocity, or the shortest penetration range. This approach was taken to estimate weapon effectiveness against the best German armor.

It is possible that the average effective resistance could be 7% to 10% less.

[ August 21, 2003, 04:47 PM: Message edited by: rexford ]

[Mr. Tittles]

I wonder if its the fact that the first plate is essentially knocking off the cap and/or reducing the point of the AP shell.

I always wondered if having an intial sloped plate would help/hurt the situation. My thinking is that shells that penetrate sloped armor take the path of least resistance. A AP shell that goes through the front of a T34 hull would basically be heading towards the floor if it did not get through the plate with adaquate velocity. It 'ricochets' downward.

[mchlstrt]

I actually read these sorts of threads but I generally have absolutely nothing useful to contribute. Thought this might be interesting, tho.

I'm no expert, but I've done a lot of soundproofing. One is essentially trying to design a barrier that a given amount of Energy can't penetrate. To oversimplify a basic priciple in that field a bit, multiple layers of varying material are superior to solid layers that are equal in whatever measures you apply (thickness, mass, etc.). I think of this as making the Soundwave burn off extra energy by 'shifting gears'.

This would make sense to me in the Armour case because you're seeing The FH Layer, a Homogenous Layer of a certain thickness, maybe a small Air Gap (does wonders in soundproofing), another FH Layer, & a Homogenous Layer of a different thickness. I would be surprised if it wasn't superior to RHA as Soundproofing, anyway.

Also, as in your Field, you can put up enough Mass to stop anything, but it's genarally not practical.

strt

[Bastables]

Originally posted by Mr. Tittles:

I always wondered if having an intial sloped plate would help/hurt the situation. My thinking is that shells that penetrate sloped armor take the path of least resistance. A AP shell that goes through the front of a T34 hull would basically be heading towards the floor if it did not get through the plate with adaquate velocity. It 'ricochets' downward.

Path of least resistance is up/down into the air away from the sloped armour, unless cap designing and T/D ratio is in favour of the shell/shot.

[JasonC]

"possible that the average effective resistance could be 7% to 10% less"

In other words, 74-76 or like 75mm about, aka about 95% quality, instead of 82mm. Which happens to be the dispute over whether Russian 76 can penetrate at 500m or can't at all.

I don't think the highest velocity impacts at ~30 degree angles are necessarily representative. There is a lot of extrapolation going on, not obviously the best way to answer the question.

The rounds penetrate without side angle, right? So why not increase the range until they fail, to get an estimated effective thickness, instead of increasing the angle until they fail, still at close range?

I'd expect the latter to show extra benefits to hardness compared to the former (highest velocity and skidding, should increase both shatter and glancing effects, which could be T-D sensitive etc).

My impression remains a Scottish "not proven". To convince me 30+50 resists like 82 rather than 75, what you'd need is a straight ahead shot consistently failing at the right range for 82 rather than 75, especially with US 75 and Russian 76 (that is, T-D close to 1, not 1/2).

This is after all the case that occurs critically in actual CM duels. If 30+50 actually bounces US 75 and Russian 76 straight ahead, at say 300-500 and 100 respectively, there should be unambiguous tests that say so, not extrapolations from different angles, shell diameters, hardnesses, etc.

For the rest of the speculators, understand that the standard models all predict marginally *lower* performance from layered plate, not higher. That is why battleships aren't layer cakes. The typical effectiveness for the weight can be as low as .85 times a single plate for 2 of equal thickness.

The issue is whether this ordinary relationship seen with homogeneous plates being layered, changes dramatically when it is instead face hardened plates being layered. Rexford claims it does. It makes mid war German armor uber if it is true, especially vs. Russian 76mm.

Explanations that expect layering generally to be useful (for imaginary air gaps and cap striping and what not) are not going to match reality, because they would all predict superior performance of layering even with homogeneous armor. Which is known to be false.

Unless the explanation is tied to face hardening and layering combined, it will give incoherent or false predictions. Note that caps are usually considered the solution to face hardening, and everyone agrees uncapped AP underperforms against the plates in question.

But Rexford is maintaining that even Russian BR-350B and US M61 APCBC underpeform against layered face hardened plate - 30+30, 20+50, and 30+50. It is a critical claim for mid war match ups and extraordinary from the standpoint of the usual models. It thus qualifies as "important if true". But to my mind, anyway, also demands extraordinary evidence.

[ August 24, 2003, 05:00 PM: Message edited by: JasonC ]

[rexford]

"Unless the explanation is tied to face hardening and layering combined, it will give incoherent or false predictions. Note that caps are usually considered the solution to face hardening, and everyone agrees uncapped AP underperforms against the plates in question."

Well, with layered armor the first face-hardened plate destroys the armor piercing cap, and then a capless projectile hits the second face-hardened plate.

So one could speculate that two face-hardened plates are better than one (by the way, the total face-hardened layer thickness with 30mm/50mm is greater than the thickness with a single 80mm face-hardened plate).

Anyway, Miles Krogfus has some microfiche with German firing test data against layered armor and he is researching the material. Perhaps we will soon have something substantial and supported in depth.

[rexford]

"For the rest of the speculators, understand that the standard models all predict marginally *lower* performance from layered plate, not higher. That is why battleships aren't layer cakes. The typical effectiveness for the weight can be as low as .85 times a single plate for 2 of equal thickness."

But are the standard models for homogeneous or face-hardened armor?

And, naval face-hardened armor is MUCH DIFFERENT than tank face-hardened armor.

With Naval face-hardened armor, the resistance is less than with homogeneous armor at high impact angles from plate perpendicular, but the opposite is the case when U.S. APCBC is fired against both types of tank armor.

Naval and tank armor have different face-hardening depths and characteristics so one can't use the standard naval models for layered armor with FHA.

We need actual firing test results against tank face-hardened armor that state the impact angles and are based on 50% success.

I also restate somethings from a previous posting that is pertinent and needs to be kept in mind:

1. the driver plates on a StuG III are bolted and are relatively small areas, so edge effects come into play and will reduce the effective resistance

2. German face-hardened plates were not face-hardened around the edges, so if the total area of a plate is small the homogeneous areas make up a greater percentage (and these are the areas that suffer from edge effects).

3. hits on the front of a StuG III have a chance of hitting the upper superstructure than the driver plates, where the resistance could allow 500m penetrations by 76.2mm APBC.

4. 500m could be the range where a high percentage of frontal hits land on the 50mm face-hardened gun mantlet

I do not believe that there is a direct relationship between 500m penetration vulnerability and the resistance of the 30mm/50mm driver plates, cause there are other areas that are more likely to be hit inside 500m.