Armor quality of Panzer III and IV

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Avalancheon
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Re: Armor quality of Panzer III and IV

Post by Avalancheon » 04 Nov 2020 00:32

Peasant wrote:
22 Oct 2020 09:37
Alright I've been meaning to do this since the beginning of this week, and finally I got time to do it. I've translated this text with automatic tools first and then proof read it fixing the most egregious issues but let me know if anything is unclear:

It so happened that in the fall of 1939, two damaged German tanks were discovered and secretly removed in Poland, which were carefully examined during the following year at the NIBT testing grounds. The PzKpfw II light tank was almost intact, but did not cause any particular emotions. Was of note the use of 15-20 mm sheets of cemented armor for protection, a successful engine design (the engine was transferred to the Yaroslavl plant for study in order to develop a project for a similar product with a capacity of 200-250 hp), a gearbox and a cooling system, but in general the tank did not overly impress the soviet examiners.

A completely different impression upon closer examination caused the PzKpfw III, referred to in the ABTU documents as the "20-ton Daimler-Benz medium tank". With a mass of about 20 tons, it was protected by 32 mm cemented armor, had a compact 320 hp gasoline engine, with a well designed power and cooling systems, excellent observation devices and, most importantly, a commander's observation cupola on the roof of the turret. Apparently, it was not possible to restore the indicated tank to a running conditions, since in the spring of 1940 the armor plates of its hull were tested by shelling from anti-tank guns and anti-tank rifles. And in 1940 the same model of tank, only fully serviceable, was bought in Germany and delivered to Kubinka for mobility trials.

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General view of the PzKpfw III Ausf G. 1940 tank purchased in Germany.

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A cut fragment of the 32-mm side armor of the PzKpfw III tank after firing with a series of five 45-mm shells (2 holes). The meeting angle is about 30 degrees. 1940.
This is interesting.

Before you published this article, I was aware of only a single Panzer III being tested by the Soviets in 1940. But thanks to you, I now know that they had tested two Panzer IIIs during this period: One they captured in Poland, and one they purchased from Germany.

Both tanks were subjected to ballistic tests, and the results were completely different in each case. To summarize: For the test on the first tank, the armor performed well and sustained 5 shots without cracking (but it was pierced twice). For the test on the second tank, the armor sustained only 1 shot before cracking (although it was not pierced). []

Both of the Panzer IIIs were shot at with the 45mm M1932 anti-tank gun. The different results may be due to variations in the quality of the Soviet ammunition, which was pointed out in the article you translated.


[] CriticalMass and I discussed these tests on this same thread. The article can be found on tankarchives (which is notoriously biased). This is it here: http://www.tankarchives.ca/2014/02/pziii-armour.html

Peasant
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Re: Armor quality of Panzer III and IV

Post by Peasant » 20 Nov 2020 10:31

An interesting thing I've noticed: in September-October 1942 trials the soviet 45mm gun actually managed to perforate the frontal armour of a Pz.IV (50mm) at a slight angle (14 + 20°) at 50m and although no complete penetrations were achieved at 100m, there were noted circular cracks appearing on the rear of the plate 50mm in diameter, which I interpret as punching starting, so this defeat was not a one time thing.

Although the failure of high velocity 45mm gun to pierce Stug's frontal armour under same conditions could be attributed to the shatter gap manifesting when shooting these shells at higher velocity than they were designed to, the effects of normal 45mm gun against Pz.III with 30+30 frontal armour are equally poor, only 15mm dents as opposed to 25-30mm impressions left in Pz.IVs armour.

According to Jentz's "Panzertruppen" the germans credit this gun with penetration of 42mm/30° at 100m, I assume against RHA using german 5/5 criteria so if the 50mm plates on this Pz.IV were not face hardened these results make sense.

Although the practical difference in protection between RHA and FHA is not very significant against soviet 45mm gun, this could alter the results quite a bit when fired at by british 2pdr gun.
Edit: Now that I think about it, maybe I'm not the first person to have noticed this. Perhaps at this point in war(1942) someone in change on the german side realized that 50mm of RHA is almost as good as 50mm of FHA against the short soviet 45mm guns.

using the 42mm/30° data point I estimate the performance of 45mm soviet ATG at 100m as: 52mm/0° RHA for reliable perforation and 58mm/0° as completely safe.

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Peasant
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Re: Armor quality of Panzer III and IV

Post by Peasant » 27 Nov 2020 00:39

I'm posting a chart containing in graphical form the data on penetration performance of the soviet 45mm AP round reported by Jentz, as well as my own estimates of its performance based on it.
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Peasant
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Re: Armor quality of Panzer III and IV

Post by Peasant » 27 Mar 2021 20:17

From this schematic it looks like the US method of hardening didnt penetrate deep enough into the shell material to uniformly harden the nose of this M62 76mm shell, leaving a large soft spot inside. But, maybe, this would work better with smaller calibers, like the 37mm M51 APCBC shot because of smaller section thicknesses involved. It certainly didnt have much issues defeating pretty hard 320-360BHN 50mm armour plates on german tanks.
This would also imply that the larger caliber shells, like the 90mm M82 APC would have even more trouble staying intact.
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critical mass
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Re: Armor quality of Panzer III and IV

Post by critical mass » 28 Mar 2021 13:06

It´s actually the other way around. The sheath hardening pattern shown above was a naval hardening technique (used only by the U.S.N. and the German navies with a lot of 15" A.P. made by the U.S. for the french BBs in 1943 also beeing of this technique) developed for major calibre A.P. It´s quiete benefitial with large section thicknesses but becomes a source of problems as the calibre goes down. The principal reason for this is that You can scale a projectile up or down but You cant scale molecular bonds in the same way. What matters in the end is that the soft spot under the nose in major calibre A.P. is covered by deep enough hardened martensite (= large quantity of longitudinal molecul bonds) but the smaller the calibre the less these bonds are creating more and more opportunity for shear failure, inducing breakage as the initial impact shock wave traverses the projectile and reflects from the base. A deeply through hardened cap assists, too, but reduces penetration.
The German Army tries sheath hardeneing pattern for its A.P. projectiles, too, but recognized it demonstrated no advantage in calibres of 10.5cm or below and a came with a definitive disadvantage in calibres of 7.62 cm and 7.5 cm or lower, compared to more conventional, decremental hardening techniques. As the calibre went up, nose hardness could be reduced.

The US Army Ordnance on the other hand kept the Navy hardining pattern down to 37mm, not because of test results but because it was considered to be the latest Navy advantage. Apparently, they failed to notice that in anti tank projectiles of 90mm and less calibre, it came with disadvantages. Lessons were learned and after the end of ww2 the hardening pattern reverted to decremental, greatly reducing break up and shatter events. Which is actually quite fascinating, because the U.S. Navy seems to have know this in advance and produced its 3" Mk. 29 A.P.C. in conventional decremental hardening pattern since quiete a while (unlike majore calibre 6" to 16" A.P.C., for which sheath hardening was employed) and with good results to be sure, but the Army preferred the "Navy sheath hardening pattern" and somewhat messed up its wartime 3" M62 A.P.C. ammunition.

I am not convinced that 37mm M51 (plain projectile body without windscreen, fuze and AP-cap, filler loaded to weight) could penetrate intact through a thick enough and soft RHA plate (for example, against 2" S.T.S. plating (270 BHN) only two out of ten test shots did not experience full shatter):
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Peasant
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Re: Armor quality of Panzer III and IV

Post by Peasant » 28 Mar 2021 22:00

critical mass wrote:
28 Mar 2021 13:06
-- snip --
Well, you know more about these things than anyone else around here, I'll take your word for it.
I'm not sure you'd bring the performance of M51 shot with it's cap removed into the mix, it would clearly perform very differently than the service ammunition against thick targets.
I know that in the trials conducted by soviets this gun+shell combination were unable to defeat both the frontal armour of a StuG as well as the 25+25mm armour on a Pz.38(t) tank beyond 100-150m range. This goes in stark contrast with the results of trials conducted by the british in NA where this weapon has supposedly defeated 50mm armour at german Pz.III tanks at up to 600yrd., which is quite close to the limit estimated for an intact shell(750yrd.). You think it has something to do with the difference in temperatures between the two locations? Perhaps a lower temperature might've increased the susceptibility of the attacking AP shells to fracture, which has proven to be decisive as they were already at the edge of their structural integrity at these striking velocities.

critical mass
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Re: Armor quality of Panzer III and IV

Post by critical mass » 29 Mar 2021 09:01

If its close enough to the actual velocity limit, and ignoring ambient temperatures (which also affects plates, ofc), penetration becomes, what others have labelled as a "stochastic problem". We know this is true. Unfortunetely, frequently we are interested to frame armor and plate dynamics as a finite solution problem with a value determinable through experimentation and calcuation. It would probably be useful to add a value for std deviation in addition to mean penetration velocity to arrive with a better understanding. I suspect that many of the "outliers" we discuss are in practice just accountable deviations in quality.

Peasant
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Re: Armor quality of Panzer III and IV

Post by Peasant » 07 Apr 2021 16:09

critical mass wrote:
29 Mar 2021 09:01
If its close enough to the actual velocity limit, and ignoring ambient temperatures (which also affects plates, ofc), penetration becomes, what others have labelled as a "stochastic problem". We know this is true. Unfortunetely, frequently we are interested to frame armor and plate dynamics as a finite solution problem with a value determinable through experimentation and calcuation. It would probably be useful to add a value for std deviation in addition to mean penetration velocity to arrive with a better understanding. I suspect that many of the "outliers" we discuss are in practice just accountable deviations in quality.
Another reason why the 37mm M51 APC shot might be more successful at staying intact is because it's a solid shot. Not because of the cavity weakening the structure, since most failures at low obliquity impact take place at the nose/body portion of the shot, but because it's more compact.

It's mass is concentrated into a shorter length and, from what I know, the bending moment to which an AP shell is subjected is proportional to the square of L/D ratio. Therefore I believe it would more successful in resisting breakage/deformation under oblique impact, all other variables being equal.

Although since its a smaller caliber it's usual targets use plates tempered to a higher hardness so in practice there might be not much of a difference.

Edit: Scratch that, the L/D ratio of M51 shot is higher than that of 75/76mm shell 2,41 vs 2,18. Here I'm considering length of an equivalent cylinder with density that of steel 7,84g/cm^3.

Thoddy
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Re: Armor quality of Panzer III and IV

Post by Thoddy » 10 Apr 2021 22:43

The German Army tries sheath hardeneing pattern for its A.P. projectiles, too, but recognized it demonstrated no advantage in calibres of 10.5cm or below and a came with a definitive disadvantage in calibres of 7.62 cm and 7.5 cm or lower, compared to more conventional, decremental hardening techniques. As the calibre went up, nose hardness could be reduced.
The tip of the 38 cm Panzersprenggranate had a hardness of ~ 59 Rc , not exactly a soft tip. And this hardness continues over the shoulder then reducing over the projectile body.
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The "german sheat" includes the tip of the projectile
(According E. Wagenknecht- Bochumer Verein -"Die Fertigung von Panzergeschossen."
Screenshot_20210411-003313_Drive.jpg


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The 62 Rc Hardness figure at tip and shoulder for 7,5 cm Pzgr 39/43 was essential for high obliquity performance( 60 degrees obliquity = 30 Grad Auftreffwinkel). Required in accordance of the somwhat harder "Standard Army armor". See also "SUPP 9/910 The penetration of armour plate" , there is a paragraph regarding optimal hardness.


It was a "optimal value" later approved by british ballistic research (DEFE 15-452 A Fundamental Investigation into the Optimum Hardness for a Capped Armour Piercing Shot) Experiments were done with two pounder shots.

For this type, the increase of hardness of projectile above Rc 62 increases projectile performance with given geometry at normal angle, but reduces high obliquity performance by early shatter. And also lower hardness reduces projectile performance by deformation (banana like bending) at high obliquity attack.

Standard projectiles with tip turn to plate when impacting plates. Adequate design of projectile shape reduce the turning moment depending on the position of the center of gravity of projectile.
turning of projectile on oblique impact.jpg
The reduction of the turning moment can also be achieved by adding a cap to a projectile that normally turns to plate during oblique impacts.
Winkeldurchschlag.png
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