Churchill Infantry Tank.

World War II British Military
#101

I’m no metallurgist, but I agree with you, my friend, that hardness and resistance are very different things.
Hardness, in it’s nature, eventually risks to become simple brittleness.
Resistance (by contrasting comparison) may lead to an eventual defeat of the plate, but that defeat will only be achieved at the considerable cost of ensuring a series of consistent/repeated pressure/hits on the same given weak spot, whereas:
Brittleness/hardness means it only takes one or two massive applications of pressure on the same weak spot to produce a defeat of the plate.

EDIT:
What the British seem to have fortuitously stumbled upon with the Churchill tanks is the beneficial results of layering steel plate.
The various turrets of the various marks of Churchill attest to that.
From what I can gather, the British initially considered the benefits of layering to be a side-effect at best, and only later came to realise they had stumbled upon a truely beneficial thing.
In post-war years this saw its’ most full expression in Chobham armour, to which the Stillbrew Armour as applied to Chieftan tanks contributed very heavily. As Chieftan was an outgrowth/development of Centurion, the link back to WW2 and the Churchill turrets is easily seen.

Kind and Respectful Regards Panzerknacker my friend, Uyraell.

#102

[INDENT]It’s not only the composition of armor. It depends also on the way you assemble it (inclination of armored plates and how you connect them, poor types of soldering means that italian tanks can be breaked in two parts with only a anti-tank rifle round in the right spot).

Well the italians used riveted combination of rolled plates, but apparently the italian rolled armor wasnt equivalent to rolled armor of other countries, USA for example, so…

I’m no metallurgist, but I agree with you, my friend, that hardness and resistance are very different things.
Hardness, in it’s nature, eventually risks to become simple brittleness.
Resistance (by contrasting comparison) may lead to an eventual defeat of the plate, but that defeat will only be achieved at the considerable cost of ensuring a series of consistent/repeated pressure/hits on the same given weak spot, whereas:
Brittleness/hardness means it only takes one or two massive applications of pressure on the same weak spot to produce a defeat of the plate.

You are in the right way, incidentally I am mettallurgical and machine-tools technician, in that I work and teach so I can write this with a pinch of confidence.

Excessive hardness brings another undesirable characteritics for armor purposes, the “back spalling” of the plate after being hit 4 o 5 times, sometimes a shower of small metal chips injuring the crew inside. A clasical trouble find in german late war armor.

[/INDENT]

#103

Thank you, Panzerknacker my friend, for confirming my thoughts on hardness versus resistance.
The spalling issue is not one that is often discussed, but has clearly been taken account of in design engineer circles, as we have the example of the various anti-spalling compounds employed in the T72 and in western vehicles in the equivalent role. The use of ammunitions designed to employ spalling as a kill-factor of enemy crews during the latter half of WW2 highlights the issue/topic.

I’m largely unaware of any anti-spalling compounds or materials as employed in WW2 tanks, apart from the occasional use of “fire-proof” rubber compounds in certain cases, the Stuart M3 being one such.

I’d be interested to see a thread evolve on the topic of anti-spalling compounds and other linings employed in the crew areas of tanks.
Admittedly, it is an esoteric topic, but one I regard as relevant to the employment of tanks in combat.

Kind and Respectful Regards Panzerknacker my friend, Uyraell.

#104

This fellow explains the situation in everyday, easy to understand terms.

"The face-hardened formula I use is in its most basic form is: “T = (C)(W^0.2)(V^1.21)”, where “C” is similar to “K” (uses quite different values for various parameters that make it up, however), above, “W” and “V” mean the same thing, and there is only this one set of exponents 0.2 and 1.21 for W and V, respectively. Note that the weight’s 0.2 power is much smaller than the striking velocity’s 1.21 power (the latter gives an equivalent p-value of 0.605, which is halfway between the most widely-used average homogeneous armor p-values of 0.714285 (giving a V-exponent of (2)(0.714285) = 1.42857)–used with the ubiquitous De Marre Nickel-Steel Armor Penetration Formula of 1890–and 0.5 (giving a V-exponent of 1.00), which is the p-value used for an ideal punch cutting out a cylindrical, full-plate-thickness, full-caliber-width plug of steel from the plate at right-angles (“normal”) impact obliquity). The small exponent 0.2 for W means that changing W (by lengthening the projectile or making the explosive cavity smaller) has rather little effect on penetration, all else being kept equal, while changing V has a large effect. This definitely is NOT a total-kinetic-energy-dependent formula using the full projectile weight W, since only the weight at the front of the projectile contributes much to the shockwave-induced breaking of the face layer that is the most important part of defeating a face-hardened plate–the base of the projectile doesn’t even “know” the projectile has hit the plate face until the punching through of the face layer is all over with! If the face-hardened plate’s soft, ductile back layer were not there to act as an “shock energy sink” to keep the hard, brittle face from shattering, the weight exponent would probably be even smaller than 0.2! Much different from the homogeneous armor penetration formula set! " (Note: the forgoing is meant to be humorous)

#105

:smiley: OK, I --managed-- to comprehend the above, but oyyy gevayyy: Mann habst nich der Doktorat ins Metallische Physik. :slight_smile:
I’d be trying hard to write the above out in much simpler terms TG, and I am laughing, sitting here, but I’d greatly enjoy seeing the corroborative Homogenous Plate Formula.

Kind, Warm, and Respectful Regards TG my friend, Uyraell.

#106

Ask, and you shall receive…

The formula for homogeneous armor penetration is “T = (K)[(0.5)(W/g)V^2]^p”, where “T” is the thickness of plate barely penetrated (by whatever definition of “penetration” you want to use), “K” is a constant (a “catch-all” that changes with projectile nose shape, projectile size, projectile damage, definition of “penetration,” plate type, and obliquity angle of impact), “W” is the projectile’s total weight, “g” is the acceleration of gravity to change weight to mass (inertial resistance) (NOTE: “g” factor is not needed if the weight is in KILOGRAMS, which is already a measure of “mass” and has the “g” division built-in), “V” is the striking velocity, and “p” is a constant–usually between 0.5 and 1.00–that raises the entire projectile total kinetic energy value “KE = (0.5)(W/g)V^2” to a single power as a unit (p does NOT change with projectile properties (other than nose shape), plate type, or obliquity angle, though). Both K and p are good for only a limited range of plate thicknesses, with up to 5 combinations of K and p needed to handle the entire thickness range from paper-thin plate to bank-vault-door thickness for some projectile designs even with no projectile damage. Note that in this formula the two terms W and V^2 are of equal importance, as in any true KE-dependent penetration formula.

#107

May many Good Blessings arrive upon thee, TG my friend.
The above is a rollicking good companion piece to the Face-Hardened Plate precedor. :smiley:

Again, I --managed-- to comprehend it, withal that I lack our friend Panzerknacer’s expertise in the topic. :slight_smile:

On a serious note, though: I can but ponder the amount of toil devoted by metallurgists of all combatant nations in WW2, attempting to formulate armours that gave their crews a little bit better hope of survival over that of the opposing crews.

Which, if it can be said to have had a stand-out feature beyond the fortuitous virtue of the adaptable chassis, the Churchill Tank did possess in reasonable degree. The vehicle could, and frequently did, absorb punishing damage in combat that nonetheless allowed its’ crew to survive.
In truth, very few other British tanks can claim the same, the Matilda (II) being the possible exception.

Warm, Kind, and Respectful Regards TG my friend, Uyraell.

#108

Face hardened armor is best against solid shot, and HE shell, but once HEAT ,and Sabot munitions became standard for basic load items F.H. armor was no longer a benefit, and not worth the extra cost of producing it. Then it was homogeneious armor. This armor while tough, and resilient, allowed passage of an incoming strike without flying apart in shards, and shivers.(well, to a point anyway) And it reduced the spalling effect of HESH, and HEP munitions (again, to a point.) Since it was not possible to defeat these munitions, the best hope lay in reducing their secondary mischief. The idea being to hopefully preserve as many of the crew as possible.
Part of the face hardened problem was by what method is the hardening accomplished. one can roll out a higher carbon plate, (the property of hardness is a function of carbon content, and its distribution within the grain structure of the metal.) or one can carburize the surface of a plate of lower carbon steel to achieve a similar result. Although carburizing may result in a less stable transition from the hard layer to the tougher supporting metal beneath it.

#109

Which raises an interesting thought, TG my friend.
Does layering various combinations of face-hardened and,homogenous plate, possibly admixed with various ceramic and rare metal compounds actually achieve the benefits the process suggests, despite its’ complexities?

What I have in mind here, is the difficulty inherent in achieving a uniform bonding between the layers, and then having said bond maintain under the pressure of repeated strikes to the outermost plate.

The Churchill never had such issues, of course, it being that most were mongrelised by ad-hoc plating being added either in factory or in the field workshops, and thus only the relative strength of the welding involved remained relevant to the uniformity of bond between layers.

Kind and Respectful Regards TG My friend, Uyraell.

#110

As far as ceramic components being used in armor that would be something relevant to Chobham armor of which I know nothing of substance. The M1-a1 uses Chobham, and the Bradley fighting vehicle uses some manner of muti layer composite armor. Having layered metallic armor gives the benefit of a kinetic projectile having to break, and penetrate each individual layer of steel while attempting to retain sufficient energy to pass into the Hull, or turret and cause damage and casualties. Its the same as shooting through a wood plank, Vs. a phone book, or body armor. Each layer absorbs energy from the projectile, and subjects it to torsional, and compressive stresses. Then the next, and the next. Having a space between layers can impose enough stress on a projectile to break it up, and it then loses its mass, and energy. (along the lines of light passing through glass.)
The term" hardened layer" in my last post means that in a single plate, only a certain depth of the steel has been hardened, the rest of the plate is normal. As distinct from 2 or more layers of plate one over the other. Also, for your enjoyment, a pic of a 4" (100mm for you Metricans out there,) target plate converted for ventilation.

4-in%20armor%20plate.jpg
4-in%20armor%20plate.jpg1760×1168 199 KB

#111

Many Thanks TG my friend, my understanding of armour has somewhat improved.:slight_smile:

The ventilated 100mm plate is an interesting, if somewhat thought-provoking objet-d’art.

One would hope to not be within auditory range when the various impacts of that plate took place.

Warm, Kind, and Respectful Regards TG my friend, Uyraell.

#112

I found some High Brow discussions of the metallurgy of armor, just a cut and paste. Note: BHN stands for Brinnell Harness Number. There are several different scales for measuring hardness, the more familiar are Rockwell
Brinell
Vickers
Knoop
Shore
Mohs Mostly used in mineralogy
Barcol

Subject: Griddling that armor
From: Robert Livingston
Date: 8/20/98 7:00:01 PM

If by griddling you mean marking by filing, the answer is that the harder
types of armor will resist files and the softer types will not. US WWII
armor was of the softer type, about 250 BHN, while most other nations
used harder steel. Files are usually case hardened high carbon steel,
and should cut armor up to 375 BHN or so. Russian tank armor was at
400-450 BHN during the later stages of the war; the 1941 and '42 KV was
around 250. German armor started the war very hard, then lost hardness
as thickness and production quantities increased. The Germans used
face-hardened armor at first, with file-resisting hardness, then dropped
the face hardening and relied on the core hardness of 250-300 BHN,
similar to US tank armor. Late-war German armor on the front of a
Jagdpanther was measured at about 200 BHN, as was Hetzer side armor. The
Elefants were measured in the low 200’s after capture by the Russians, as
early as 1943. These are the softest examples of German armor I can
recall. I would expect easy filing on them, and maybe easy griddling,
too.

Generally, hard armor is expected to break up attacking projectiles,
which it can do when it is thicker than the diameter of the projectile.
Soft armor is best at absorbing projectile impact through slower
deceleration. The switch from the earlier face-hardened or
hard-all-the-way-through steel came about when the major combatants
introduced penetrating caps on their ammo, which protected against
shatter when hitting hard surfaces. These caps were so effective that
the FH armor resisted less well than softer homogeneous armor.

Armor under 375 BHN is called Machineable, which means that it can be cut
with normal machine-shop cutting tools. The harder it gets, the more
often you have to sharpen the tools, until you get to a hardness which
resists cutting completely. Tungsten carbide has been used to cut the
harder steels without excessive resharpening. By the same token, TC was
(is) used for armor-penetrating projectiles; during WWII there was
constant tension in Germany between those who thought it should be
reserved for the machining of steel and those who thought it should be
used on the battlefield for the penetration of armor.

#113

Impressive as usual, tankgeezer. I am often awestruck by the knowledge available on this forum. Glad I joined.
Now, about the Churchill. On this thread, many have derided it, and many have lauded it. So as not to be redundant, I stand on the side of admirers. Way to go, Britts!