Armor flaking?

[dd77]

What exactly does it take create flaking? (I know what it is) Lets say you have a 60mm plate, nothing fancy, and its struck head on (90) by some round but doesn't penetrate. How "hard" does that round have to hit for there to be a chance of flaking and is there any where I can read up on the finer details?

[flamingknives]

The effect is technically called spalling. Doing a search on that term will get you more results.

The impact has to be sufficient to create shockwaves in the impacted plate such that the release waves caused when the shock reflectes off the free edge of the struck plate it can combine to exceed the ultimate tensile stress of the material. As the superposition of release waves is important, the location struck in relation to free edges is important, as are material properties. I can't give any numbers, as I'm just familiar with the theory. 'Hard' would be measured by energy, which is a function of mass and velocity.

[John D Salt]

Originally posted by flamingknives:

The effect is technically called spalling. [snips]

Also known as the Hopkinson effect. Monroe and Misznay & Schardin get their names on their warhead effects, so why shouldn't poor old Hopkinson?

All the best,

John.

[MikeyD]

Generally, the higher the hardness number for the armor the more likely it is to spall. When soft armor is penetrated the hole tends to 'petal', basically the surrounding material bend out of the way of the shell. High hardness armor shatters. I've seen pictures of 6 pdr penetrations to a Tiger I side where a dinner plate-size piece of jagged metal has broken off the inside armor, like a flying circular saw blade! Probably does as much damage to the interior as the shell itself.

'Dual hardness' armor is the best of both worlds. Face-hardened armor has been heat treated so the outside face is high hardness while the inside is more ductile. The modern equivalent might be those bolt-on high hardness ceramic on APCs. Russians were pleased with their lend-lease Shermans because late war U.S. armor produced very little spalling compared to a T34.

[flamingknives]

The Professor who taught me about it called it spalling, so that's what I call it. If the Hopkinson effect is analogous to the Monroe effect, should it not only apply to HESH-type shells?

Hard armour doesn't have the plastic deformation that soaks up energy. It reaches it's tensile limit and fractures instead.

[MikeyD]

British HESH (squash head) shells relied entirely on spalling effect. No need to go through all the trouble of penetrating the armor if you can simply break a big piece off inside and send it spinning through the fighting compartment! Didn't the Russian SU-152 have a big concrete breaking round that had about the same effect on armor?

[dd77]

I've seen it called both flaking and spalling, and in game the message is says flaking, so I used that. At any rate, I know what it is in general, but I'm looking for more specifcs on how to approximate/guestimate what rounds may or may not cause flaking/spalling on various armor types / thickness. IIRC HESH was originally designed to be used against concrete fortifications (which works well) and it was soon found out that it worked very well vs tanks due to spalling. Modern armor seems to be able to deal with HESH rounds well however. Anyrate, thats a tangent. Back to where I can get the details

[JonS]

Huh - you learn something new everyday. I had thought that spalling and flaking were different - to wit:

* Spalling described the bits of armour that break free from around the hole when a round completely penetrates.

* Flaking, OTOH, was the bits of armour that broke free from the inside face due to a non-penetrating hit (or a HESH hit, which IIRC isn't meant to penetrate anyway).

But apparently not

Cheers

JonS

[ May 27, 2004, 05:37 AM: Message edited by: JonS ]

[stikkypixie]

Originally posted by dd77:

I've seen it called both flaking and spalling, and in game the message is says flaking, so I used that. At any rate, I know what it is in general, but I'm looking for more specifcs on how to approximate/guestimate what rounds may or may not cause flaking/spalling on various armor types / thickness. IIRC HESH was originally designed to be used against concrete fortifications (which works well) and it was soon found out that it worked very well vs tanks due to spalling. Modern armor seems to be able to deal with HESH rounds well however. Anyrate, thats a tangent. Back to where I can get the details

You mean in CM it self?

[MikeyD]

A least in the game it seems flaking (spalling) is more a function of how brittle a particular vehicle's armor is, as opposed to which type of round strikes it. I've seen 75mm shells strikes produce flaking and 37mm shell strikes produce flaking.

Its hard to tell which Allied vehicle in CMAK flakes because most armor immmediately explodes! I've seen pretty high flaking on late war Panthers and StuGs in CMAK (due to German steel industry shortages in materials like chrome, I believe) and the T34 in CMBB which was always made of high hardness steel.

Is anyone keeping track of who flakes and who doesn't?

[jrrich0000]

An addition: spalling is caused by kinetic energy from the impact (or detonation in the case of HESH) causing the armor plating to fracture along the crystallization lines in its structure. Harder steel in general has greater crystallization, so harder steel in general causes more spalling.

The Army calls it spalling whether the round penetrates or not.

[dd77]

Wonder if we can get a dev in here to put some light on how they calculate it (specifics) or the sources they used.

[flamingknives]

Originally posted by jrrich0000:

An addition: spalling is caused by kinetic energy from the impact (or detonation in the case of HESH) causing the armor plating to fracture along the crystallization lines in its structure. Harder steel in general has greater crystallization, so harder steel in general causes more spalling.

The Army calls it spalling whether the round penetrates or not.

Harder steels have finer crystals, but greater spalling occurs with material that are not crystalline in proportion with their hardness. The energy of the impact generates shockwaves, which by definition are in excess of the elastic strain limit of the material. The harder the material, the smaller the difference between the elastic and the ultimate stress, so there is less plastic deformation to soak up the energy carried by the shockwaves.

[dd77]

one more punt for the physics/formulas

[Sergei]

And I thought armour flaking was what Germans did with those 88mm guns to the Allied tanks...

[flamingknives]

Originally posted by dd77:

one more punt for the physics/formulas

Hey, what am I posting, the sports pages from teletext?

Formulas I don't have, at least not the ones you're after. The number of variables involved means that the theoretical formulae are rather complicated. There may be some empirical formulae, but these will necessarily be specific to certain plates/impacts.

[dd77]

Not sports page stuff, but not links or references to what I'm after obviously I'm not looking for general statements.

[Biochem can be fun]

Flamingknives, I appreciate that you have some materials training. Armor "strength" has always been kind of a strange term for me to understand. Strength, toughness, and hardness have very specific meanings in materials science. Strength is the amount of force to failure for a material per unit area (or the elastic strain limit as flamingknives stated). Toughness is the amount of energy that a material has absorbed at failure (obviously per unit area). And hardness, well that's a little more confusing. In my work, we're generally working with nanohardness--which is a materials resistance to plastic deformation upon nanoindentation. In a nutshell it's related to the modulus (stiffness) of a material. Hardness does relate somewhat to the toughness of a material, but not exactly. Flamingknives stated that hardness is the difference between the elastic and the ultimate stress of a material. I guess I should state that I'm generally working with biological materials, so I'm in no way a materials scientist and only understand the math at a very rudimentary level. Basically, what exactly does strength mean when one is talking about the armor plates on tanks?

Cheers,

J

[flamingknives]

I'm not exactly an armour grog, but I'd classify armour strength as:

The ability to defeat projectiles carrying a certain amount of energy. This can be achieved by deformation of the armour, or deformation/deflection of the projectile.

Energy is absorbed by deformation of a material, force times distance. In the case of deflection of the projectile, the energy transferred to the armour is related to the change in velocity of the projectile (rather obviously)

Spalling, as described earlier, is caused by superposition of shockwaves propagating through the material. The shockwaves can be modelled by the Rankine-Hugoniot jump conditions. For this you need details of the impact pulse.

The only example I can think of is that a 3mm sheet of CFRP will suffer spalling damage due to an impact of around 20 joules. CFRP, however, is vastly more brittle than the weakest steel, so that doesn't help too much.

120mm HESH will defeat a 130mm armour plate.

[Redwolf]

Is that as in real-world formular or for the game?

Like most interactions of material and shocks/impact I would highly doubt there are formulars to describe what piece of armor will go off where. If anything somebody might have an approximation formular but I highly doubt that.

As for the game formular, if you have a hit which does not penetrate you invoke a probability for spalling and if there is spalling you have a probability to hurt a crewmembers. That's all. I even doubt that CM makes a difference between different tanks and their tendency to spall (e.g. a T-34 should spall more than a Sherman).

[REVS]

Formula.

[Redwolf]

Originally posted by REVS:

Formula.

Are you talking around real-world or CM here?

[flamingknives]

I think that he's being picky about spelling.

[MikeyD]

I thought there was some conversation back in CMBB days about BFC increasing the likelyhood of late war Panther Gs to spalll due to well known armor manufacturing deficiencies. And I recall it was categorically stated that T-34 high hardness steel had a higher spalling likelyhood. So there does appear to be a vehicle-by-vehicle difference in spalling tendencies in CMBB at least (based on armor hardness?). In CMAK the differences aren't quite so apparent (no T34s). I haven't played late war HVSS Shermans much in CMAK, they should theoretically have very low spalling tendencies.

[flamingknives]

Armour hardness is modelled, witness the change of given AP values in CMAK from CMBB because the majority of armour around the Med wasn't hard/face-hardened. Adding on a liklihood of spalling proportionate to the armour hardness would seem to be simple and worthwhile.