Armor quality of the Tiger I

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critical mass
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Re: Armor quality of the Tiger I

Post by critical mass » 23 Feb 2020 11:51

Peasant,

The terminal velocity relations for 100mm come directly from ARTKOM GAU and are to be used as reference for describing distances (AP projectiles explicitely mentioned) after trial. In such more experimental trials, unlike in field trials, f.e., the actual terminal velocity was carefully measured after each shot on a test range with calibrated instruments. The gun was not put at a distance but the charge was modified to obtain a desired striking velocity. Ranges then were calculated based upon ARTKOMs velocity tables used for reference. This is what carries significance for this primary source document, because it explecitely testifies which range / velocity combinations were officially specified by ARTKOM in this period.

It is important to understand the form, in which distances are presented. After all, ARTKOM gave the remaining velocity by a table (sometimes by a formula), which it clearly stated in its official documents. Its not needed to interprete anything here, such information would lead a commander to assume he could defeat a given target, at say 1000m. I believe, they all thought so. Yet, ARTKOM didnt make clear that the actual velocity / distance relation for its reference was above the specification requirement for projectiles actually procured for service, and this resulted in a distance of a couple of hundred meters less for a given downrange velocity. Zaloga and many writers cited and continue to cite these trials unreflectedly, and I think even Bird/L. worked using the hypothesis that official distance data from actual soviet trials 1944-1945 bear close relationship to real terminal velocities. It is submitted here -as my personal opinion-, that the discrepeancy is large enough to not just constitute a minor problem for modern re-assessments of vintage period armor trials.

Of course, we do not know who was responsible for this error but it is necessary to be careful when actual terminal velocities are omitted from soviet trial data of the period 1944-1945. Distance data only are knowingly compromised and thus, may be a misleading proxy. Equally, one needs to be careful when the actual way the trial was staged is unspecified. Was the charge modified to obtain a desired striking velocity? Was the gun moved away the distance, instead? These two forms are not necessarely as compatible with each other as one might assume. Ambient temperature is relevant, as well as target condition, too, on how the armor responds.
Is it even possible to predict the interaction of shell and armour at high obliquity with so many variables affecting the results? Clearly there has to be some limits on what is possible, otherwise we would've seen photos of the UFP of KT penetrated by the soviet 45mm gun.
Is there really no lower limit on protection provided by the sloped armour (besides that it cant be less than its nominal thickness, obviously... right? at this point it wouldn't surprise me to learn that even this is not true.)
There is a difference between correlating factors and prediction. Its fairly easy to establish correlations between known datapoints but it will be difficul, too, to also predict unknown datapoints from the isolated sample of known datapoints. Since this sort of AP- vs Armor discussion revolves around historical data, of which the vast majority is either incomplete, unknown or lost, one has to eventually take the step to move away from closed form equitations. Its necessary to adopt a statistical inference, which takes into account and embraces the fact, that we can update our information and challange prior assumptions. This is better reflected, I think, in adoption of bayesian statistical modelling. This way, we probably cant pinpoint a discrete result or predict every event but we can exclude the unlikely...
Have you considered that the armour remained ductile because its structure was already compromised by a nearby hole, therefore it didnt offer as much resistance to the 152mm shell and did not absorb as much energy as an otherwise intact plate would've?
Once the plastic deformation exceeds a limit and becomes a permanent change of geometry, work hardening sets in. Work hardening increases the strain limit, but does not increase the limit of plastic deformation. Quite contrary, a high degree of plastic deformation work hardening can increase the brittle tendency due to triaxial stress risers, locally defeating the limit of plastic deformations. When this happens, one can frequently observe crack formation between two or more of the nearest boundaries (hole or plate edge). Further, the resistence to perforation is reduced by closeby boundaries (unsupported right angles and holes).
Thats why a 3 cal minimum distance between two impact points was specified in the first place in trials to allow only "fair hits". For the 152mm, this would require 0.46m distance to the next impact to be free of edge effects and cracking. Only a very ductile plate may not show brittle tendencies despite multiple, closeby impacts, and this is shown here, despite the largest possible calibre (152mm), wich constitutes the most severe form of test for ductility. It goes some way to directly contradict the interpretation of brittle behavior of german plates if engaged by large calibre AP, found in the article, no?
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Peasant
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Re: Armor quality of the Tiger I

Post by Peasant » 25 Feb 2020 19:24

critical mass wrote:
23 Feb 2020 11:51

-- snip --
cm,
that was a lot of text. took me some time to unwrap all of it. I've also went back and read some of your older comments in this thread.

I will take your note about statistical description vs prediction to heart and will take care not to extrapolate the results from one data set very far.

I'm not arguing that, under ideal circumstances, the german armour steel shows excellent performance.
Both the british trials with the 100mm shell as well as soviet testing of 85mm gun against Tiger I side armour point towards the 100mm D-10 gun not being able to reliably defeat the 85mm Panther glacis beyond 600-700m. (which means I retract my previous statement about the terminal velocities used in testing).

A good example is a test by the soviets where the captured long 88mm gun defeated the 85mm/55° Panther UFP at only 600m, while the glacis plate of the late JS-2 tank (90mm/60°)(a variant with fully welded hull) made with domestic RHA, was determined to fail against this gun already at 400m.
Another example is when in british trials of a captured Panther tank, its side armour sustained numerous hits of 6pdr AP and APC shells in a small area without cracking or caving in.

Image


But, it is also true that numerous sources point to the fact that a considerable fraction, if not the majority, of late war german armour had relatively low IZoD values and cristalline fracture, even at room temperature, ascribed by the western specialists to an improper heat treatment, which would likely decrease its performance as armour material relative to the well made examples of it.
Are you saying that they are wrong and this would not be an issue under heavy ballistic attack?

Regards, Peasant.

critical mass
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Re: Armor quality of the Tiger I

Post by critical mass » 29 Feb 2020 18:58

Yes, I have seen SUPP 22/58 reports on both PANTHER and BRUMMBÄR armor plates, which indicate that the armor tended to produce less ductile holings against 2- & 6pdr AP in normal attack. This refers to glacis as well as superstructure and turret side hits.

Depending on what one might want to require, this could be critisized, if, for example, no spalling was considered important.
However, a closer examination of the trials indicates the presence of a confirmation bias at place in the conclusions. It´s noteworthy that the british choosed 6 pdr and 2pdr AP here but not capped AP, which does not break up under normal impact so easily. Break up of the shell will cause discing or plugging, and excludes ductile holing events. Further, one might whish to ask why the plate was tested at normal in the first place. The glacis plate was an oblique armor plate, turned 55° from the normal, while both, PANTHER superstructure and turret sides were required to offer resistence at oblique, glancing hits only, not at normal attack. I suppose You are aware of the mutually inverse relationship between ideal ballistic resistence under high and low oblique impact, respectively, which formally oppose each other. Thus, by todays standards, the testing carried out under the X.908 post war trials (PANTHER armor plate) was performed under conditions, which the actual armor plates were never required to satisfy in terms of actual platform resistence as specified.

From the british perspective, It was reasonable to conduct the tests as they did, owing to the fact, that the british I.T.80E armor specifications did not contain differential specifications for armor plate intended to resist normal attack and those plates required to resist glancing blows. With this observation I relate no judgement and many nations followed such practice during wartime. For them, it was by all means the same task to be performed by the same armor. The germans, however, did make this important distinction. Their acceptance testing does specifically test at low (with large cal) and high obliquity (with lower cal) to satisfy differential requirements.
Its not a coincidence that BRUMMBÄR and TIGER-I plates were generally regarded high quality by the british, while PANTHER, JAGDPANTHER and TIGER-2 armor more often than not was considered sub optimal. The former includes normal attack in its specifications, the later did only include oblique impact in their specifications, yet the british kept testing all under normal impact in their experimental series of trials. Careful observers will have noticed here, that field trials on actual platforms did not always square off with the findings on range trials using the cut off armor plate...

Now we come to impact strength. The problem here is that during ww2, the british did not understand what caused temper embrittlement in their armor plate. For a long time, they believed it was caused in the heat and not during subsequent heat treatments. This little by little was understood towards the end of ww2 and focus shifted to heat treatment regimes in combination with Izod impact strength figures as a proxy for the presence of temper embrittlement. Spalling and cracking was easily mistaken to indicate embrittled plate, even when this was not the case. The problem here lies in the fact that the correlation between impact strength and reduced ballistic performance was nowhere straight or linear. The low impact strength proxy thus, could lead to misleading results.

There is indication in the british trials that this really did took place in regard to their assessments of german RHA. They took BRUMMBÄR 50mm RHA superstructure side plates and tested them, again with 2pdr and 6pdr at normal in the postwar X.884 trial. In this case, for an assault gun, the approach is somewhat more justified, as the design specified resistence to the sides against infantery weapons, including normal attack. The british considered the plate generally good (notice the difference to the PANTHER, which was tested out of realm!). Testing established the fact, that these 50mm plates were 5.6% above IT 80E specifications but it showed markedly lower impact toughness and tended to flake at places. Embrittlement was indicated by inferior Izod strengths, ranging from 14 to 25, far below british specifications for I.T.80E.
In order to verify this, they cut the plate in half and send parts to E.S.C for british reheat-treatement. Indeed the impact strength went up with up to 48 Izod recorded in the same plate after retreatment. Subsequent ballistic trials indeed showed less tendency to flake, so it was concluded that the re-heat-treated plate would have passed british trials with flying colours!
Yet- and this is important- The Holing ballistic limit (A.B.L) of the re-heat-treated plate was 15fps lower and the perforation limit (W/R) was 76fps lower than the ballistic limit of the un-heat treated, original armor plate.

Thats a staggering result. The improvement of mechanical properties of the armor plate -by re-heat-treatment along british ideas- actually made the plate significantly worse in terms of actual resistence to both, holing and complete perforation.
The report concludes with the words:
"In general, the results indicate that the ballistic properties of better quality German armour are not further enhanced by retreatment on British lines; but other experiments with poorer quality German armour have shown that they can be improved by correct heat treatment. -SUPP22/58, p."
Here it should be kept in mind that the germans heat treated their RHA purposefully close to the first ductile / brittle transition point for otimum ballistic resistence when normal obliquity resistence was specified. Yes, by defintion, these plates will always show less Izod strength, and frequently, will also show more marked flaking and spalling against AP at normal attack but it doesnt mean that the plates are embrittled due to the purposeful hardness point and it doesnt follow, that this will cause reduced ballistic protection in the first place.
Notice that "poorer German armor" is better understood as "German armor which performed poorer under normal impact test". Its my opinion that lower ballistic resistence under normal impact is often correlated with good ballistic resistence at high obliquity, which is the obliquity these armor plates were specified to resist in the first place.
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Avalancheon
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Re: Armor quality of the Tiger I

Post by Avalancheon » 01 Mar 2020 21:12

critical mass wrote:
29 Feb 2020 18:58
Further, one might whish to ask why the plate was tested at normal in the first place. The glacis plate was an oblique armor plate, turned 55° from the normal, while both, PANTHER superstructure and turret sides were required to offer resistence at oblique, glancing hits only, not at normal attack. I suppose You are aware of the mutually inverse relationship between ideal ballistic resistence under high and low oblique impact, respectively, which formally oppose each other.
critical mass wrote:
29 Feb 2020 18:58
Its not a coincidence that BRUMMBÄR and TIGER-I plates were generally regarded high quality by the british, while PANTHER, JAGDPANTHER and TIGER-2 armor more often than not was considered sub optimal. The former includes normal attack in its specifications, the later did only include oblique impact in their specifications, yet the british kept testing all under normal impact in their experimental series of trials. Careful observers will have noticed here, that field trials on actual platforms did not always square off with the findings on range trials using the cut off armor plate...
I remember you saying something similar in another thread. You were summarising the results of a postwar Soviet test, where high and medium hardness armor was shot at with 88mm Pzgr 39

Their conclusion was that medium hardness armor offered greater resistance at high obliquity, while high hardness armor offered greater resistance at low obliquity.

I'm guessing the Germans figured this out years before the Soviets did? Hence the different specifications for the glacis armor of the Tiger vs the Panther.

viewtopic.php?p=2231384#p2231384

critical mass
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Re: Armor quality of the Tiger I

Post by critical mass » 03 Mar 2020 10:27

The relevant thread were the section on post ww2, soviet trials using german ammunition vs their domestic RHA and HHA armor here:

viewtopic.php?t=238896

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Re: Armor quality of the Tiger I

Post by Contender » 09 Mar 2020 21:50

I cut back part of soviet test (left out tank pictures):
Image
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Image
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Can someone make out fuse what fuse the 85mm uses ( #5 on page one)?

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Re: Armor quality of the Tiger I

Post by Avalancheon » 25 Mar 2020 03:12

Specifications for the Tigers armor can be found in the book, Germanys Tiger Tanks D.W. to Tiger I. It states that the 100mm glacis plates were made either from PP7182 alloy by Krupp, or from HB75 alloy by D.H.H.V. The former had an alloy content of 2.85-4.30%, while the latter had an alloy content of 2.50-3.35%. Regardless of the alloy used, the glacis plates were always hardened to 265-309 brinell.

The British did tests on a Tiger they captured in Tunisia, using a poldi hardness tester. They indicate that the glacis was closer to 265 BHN, which seems rather on the low side. Surprisingly, the 80mm hull sides were only 265 BHN, while the 80mm hull rear was just 255 BHN. Given that these were thinner plates, one would have expended them to be harder.

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Re: Armor quality of the Tiger I

Post by Contender » 27 Mar 2020 22:44

Issue is if we take a look at the soviet 1943 85 flak gun stuff above it claims penetration (and a rather large bit of damage) of the bottom plate 100 @ 27 deg at additional compound angle of 30 at 1600 meters using a "Armor Piercing tracer round" surely this highlights a quality problem with the Tiger I plate?

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Re: Armor quality of the Tiger I

Post by Peasant » 28 Mar 2020 15:10

The 57mm Zis-2 gun firing at Tiger I superstructure side and turret armour (82mm/0°) with BR-271 shell at 900m/s muzzle velocity produces one defeat at 800m(800m/s), one defeat and one non-defeat at 1000m(776m/s) and 3 non-defeats at 1450m(723m/s).

The associated classical DeMarre K score for 1000m BL is 2409 and 2243 for impacts at 1450m, well in line with estimates.
I find it curious that even at these relatively elevated velocities the performance of blunt headed shells does not degrade more than it is for the lower velocity weapons, like the soviet 76mm tank gun.
One would be intuitively expecting the K score to get progressively higher with the striking velocity.
critical mass wrote:
03 Mar 2020 10:27
Do you have any theories on why that is?
Contender wrote:
09 Mar 2020 21:50
Can someone make out fuse what fuse the 85mm uses ( #5 on page one)?
It's the MD-5(МД-5) fuse.

critical mass
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Re: Armor quality of the Tiger I

Post by critical mass » 31 Mar 2020 18:49

Do you have any theories on why that is?
I am afraid, I am not sure to which aspect in particular this question refers.

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Re: Armor quality of the Tiger I

Post by Peasant » 31 Mar 2020 20:51

critical mass wrote:
31 Mar 2020 18:49
Do you have any theories on why that is?
I am afraid, I am not sure to which aspect in particular this question refers.
My bad. I remember you saying that once shatter sets in the AP shell, its penetration capabilities should be expected to stop increasing and even start going down as the striking velocity grows and the damage becomes more severe. But as far as I've seen this is not the case. Beyond shatter gap region, the penetration for a broken up penetrator appears to keep growing with more energy, albeit at a slower pace, so I wanted to ask: is there something I'm missing or did I misunderstand your words? :?

critical mass
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Re: Armor quality of the Tiger I

Post by critical mass » 01 Apr 2020 18:50

Thanks for explaining.

For the aspect under consideration, I dont see a problem. First of all, the terminal velocity is not known. Its not clear to me that they used service Br-271 projectiles in the firing trials. The exact type of projectile used has not been photographed and the only reference made refers to a 57mm projectile according to drawing No. 2-15589 (чертежа No. 2-15589). Such reference does not comply with any other service projectiles in this document (they did record the use of 45mm Br-240 projectiles at p10, 75mm M62 at p.22, 76mm UB-361D at p.30, among others).
I know this form from other cases, particularely for special trial shot used, f.e. to examine new armor. Such projectiles may differ in a number of details from regular service AP, (hardness treatement?) and its not known which terminal velocity data were used here (Br-271 and Br-271K differ vastly).

Further, there is no photographic evidence for a penetration at 800m, which is somewhat curious. The one single penetration photographed for the 57mm ZiS2 at 1000m is far too close to the lower edge of the armor, to be considered a fair hit. A crack actually connects the hole with the deformed, at this place, lower edge of armor. The remains of the shell shown for this hit show remains of the base of a projectile, apparently without any cavity (such would be visible here so close to the lowest of the driving bands), not too dissimilar to how the lower body of a Br-271SP (AP-shot) looks. Its likely here, that no nose-only shatter but projectile break up is witnessed. But that cannot be sure without knowing the remains of nose pieces. Generally, it can be tricky to differentiate projectile break up from nose only shatter. The basic difference is that the former takes place during the penetration while the latter takes place before onset of penetration and often is recognized either by shallow dents or if the break up disappears when one raises velocity (as the time exposire to triaxial stresses are reduced with faster striking velocity). Shatter does not disappear when one raises velocity, because shatter takes place before any meaningful penetration takes place.

If You count everything together, the only fair penetration is believed to be related to 800m, though its not secure, if this eventually was a fair hit due to lack of photo evidence. Its not clear which type of projectile was used and hence, the velocities for the De Marre K figures are speculation so far. If we follow Your terminal velocity estimates, K=2408 was somehwat too low for a fair hit. It needs to be higher and the 800m event is K=2460-2480.

Its not impossible that they used special trial shot here, which shows less tendency of break up. The depth of penetration in many cases was 45-70mm, with two shallow indentations (at 500m and 1450m) demonstrating shatter, the other do suggest break up, as did the hit at 1000m.

There were two more hits at 500m, and both failed to hole the armor. But they were placed against the 100mm front plate and against the strong point of the MG armoured Kugelblende. The velocity was too low to affect penetration, but high enough to break up (shatter in one case) the projectile.The two presumtive shatter cases, each at 1450m and 500m give a wide variance in individual projectile quality, which is not unlikely to what can be expected. It does not follow, however, That the performance is better. Notice that one indentation at 1450m was just 15mm and all indentations were 110-125mm diameter, approx. 2 cal for the 57mm, suggesting some sort of mushrooming of the projectile against the plate took place (upset or compression damage) even where no shatter damage occured.

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Re: Armor quality of the Tiger I

Post by Miles Krogfus » 02 Apr 2020 19:58

Here is page 61 of the discussed Tiger I test that shows the projectiles used.
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Re: Armor quality of the Tiger I

Post by Peasant » 02 Apr 2020 22:43

critical mass wrote:
01 Apr 2020 18:50
Good catch. Cant believe I've missed this after reading document so many times. I'm currently looking if the schematics of this unusual shell have surfaced somewhere on the russian speaking parts of the web.
And its neither shown on the photo with other shells, very curious indeed.

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Re: Armor quality of the Tiger I

Post by critical mass » 03 Apr 2020 08:24

Miles Krogfus wrote:
02 Apr 2020 19:58
Here is page 61 of the discussed Tiger I test that shows the projectiles used. Projectile #3 is the 57 mm BR-271K.
I do not give internet sites that contain pages from Soviet firing tables and firing tests my E-Mail address and other information, so only sites that do not ask for info allow me to view Russian documents. If other AHF members post here on AHF pages that I can see, they give me the opportunity to make additions and corrections based on 1930's-1970's Soviet primary material that I have.
Miles,

the photo labels under #3 an engl. 6pdr shell (which was used, too, in these trials), not the domestic 57mm.

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