Armor Plate Discussion (Robert Livingston!)

[John Kettler]

Found this while researching armor spalling. Some great stuff from Forum Member Robert Livingston (co-author of the much sought World War II Ballistics: Armor & Gunnery) and others. Very groggy stuff on types of tank armor, performance under impact, metallurgy, production methods and limitations, which country produced what and how good it was, plus much more, to include the concept of ideal armor.

http://yarchive.net/mil/ww2_tank_armor.html

On a related note, this footage of projectile impacts filmed at a million frames per second should prove most useful.

I recall reading in the above book about edge effects and really not getting it the first time through. But watch this Werner Mehl video 30 seconds in or so and learn. It makes a huge difference whether the projectile strikes the center of the target or near a plate edge. Particularly noteworthy right from the beginning is hyperplastic flow by soft homogeneous metal armor hit by a projectile at low obliquity and high velocity as the penetrator burrows into the armor. This is responsible for the characteristic petaling seen on dead Shermans hit by German PzGr 39.

Here's one such tank. Though the detail is hard to see, it's easy to note the lip around where the AP shell penetrated.

http://tinypic.com/view.php?pic=21es1kw&s=1

This Army study, though, on page C-4, Figure C-3 shows the petaling up close, so you can compare it to the vid. This do is the how-to of armor ballistics testing. Groggy as it gets, but most educational!

http://www.dtic.mil/dtic/tr/fulltext/u2/a137873.pdf

Regards,

John Kettler

[John Kettler]

I've read the entire thread at the first link, and if you're the least bit interested in armor and armor penetration, then I highly recommend taking 15 minutes or so to read that thread, in which Robert Livingston's discourses are toward the bottom. As the British say, it's cracking good stuff. I learned a great deal, and it's nowhere nearly as demanding a read as the Army study (last link of my Post #1 earlier).

Regards,

John Kettler

[ArgusEye]

It's an interesting discussion, without the baseless assertions that mar most of these threads. Good read.

I must disagree on the high-speed movies showing hyperplasticity though. There is no sign of it, all we see is small arms projectiles hitting objects. I think you refer to the bullets hitting the lead sheet, which shows the fluid looking cratering we see on tanks with soft armour. Hyperplasticity is a different phenomenon entirely.

[John Kettler]

ArgusEye,

Glad you enjoyed the discussion. I found it most informative.

Absent descriptions, we pretty much have to guess at what we're looking at. There's a sequence in the vid in which a projectile with a pointed base pierces what I believe to be aluminum plate. I know of no bullet, even a spitzer design, with a pointed base. Additionally, it looks to be made of steel, not cupronickel jacketed or straight lead. If I'm right, that is a situation under which hyperplasticity could occur (monobloc armor, perpendicular or close to it impact angle of projectile).

Regards,

John Kettler

[ArgusEye]

At 07:50 you see the same projectile hitting some actual steel. It splays open, showing it to be a simple full metal jacket bullet.

I don't think we see any aluminium used as a target. It sparks, spalls like crazy, and doesn't take much elastic or ductile strain before it cracks, and I didn't see any of that here. From 3:15 we see something that might well be aluminium.

Hyperplasticity happens if the impact is fast enough to cause dispersion of the compression waves generated by the collision in the target material to keep ductile [plastic] deformation modes for greater strains than can be achieved in quasistatic deformations. The exact mechanisms are still being studied, but the dispersion of the medium are clearly the key. Since these are momentum deformations rather than hydrostatic deformations, the Poisson effect does not contribute to changing the yield mode of the material and this allows for ductile, even fluid plasticity to occur much longer. In WWII this is mostly seen for shaped charges, as very few other projectiles and armour types even came close to this type of velocities. I am very confident we don't see any hyperplasticity here.

[John Kettler]

ArgusEye,

Having watched the Mehl video just now, I remain of the firm opinion that the first projectile impact is of a machined steel or tungsten AP projectile. The impact phenomenology sure looks to me like what's readily observable on quite a few pictures of Sherman tanks drilled cleanly through vertical side armor by 75s and 88s. What we're seeing here, in the first impact of the Mehl vid, is metal flowing under a powerful high velocity impact.

Unfortunately, the camera doesn't show either side of the plate struck after the impact and suspected complete target perforation have occurred. This makes it hard to gauge what the near side of that target looks like post penetration.

Regards,

John Kettler

[ArgusEye]

Do you disagree that the pointy-tailed projectile in the first impacts is the same as the one disintegrating at 7:50?

We do see fluid plasticity in the first few impacts, but this is due to the soft metal target, not to hyperplasticity. And normal plasticity, as here, is indeed the main failure mode of Sherman armour.

[John Kettler]

ArgusEye,

Would say the one at the beginning and the one whose external casing(?) is splaying (7:53) under impact rather like a banana gets peeled are the same projectile type, but I suspect the target is much harder than the first one. In the earlier sequence, the now apparent HVAP, if you will, punches cleanly through the target without stripping off the outer sheath. Whatever gets hit at 7:53 seems to be much tougher and appears to strip the sheath off, presumably so the core can continue through. Either that, it's an outright projectile defeat, but lacking the post shot imagery, again, it's hard to tell, at least for me.

Regards,

John Kettler

[ArgusEye]

The same target is struck by obvious pistol projectiles. There is even some footage of the pistol muzzle in the movie. And let's face it, there is no displacement or damage evident in the target material. To top it off, the splayed projectile slides across the surface of the target. Would it do that if it were anchored to a surface deformation due to a penetrating core? I find it very hard to see as anything else than a long pistol projectile.

[Freyberg]

Fascinating, especially that video

[Freyberg]

I take it the blocks of jelly-like stuff in the video are made of that forensic stuff that's supposed to mimic human flesh? Chilling if so...

[John Kettler]

Freyberg,

Technically, it's called ordnance gelatin, but is now generally called ballistics gel. And, yes, you're right, it's a human flesh simulant. That great blooming in it as the projectile strikes and penetrates is the temporary cavity. Once that subsides, the actual hole excavated is called the permanent cavity. Wounding and kill criteria are a function of depth of penetration and various other metrics.

Regards,

John Kettler

[c3k]

Well, it's not so much meant to be a human flesh simulant as much as it's meant to be a replicable impact simulant. Human flesh is very different than ballistics gel. Bones, density variation, ligaments, tissue, etc., are VERY different. However, ballistics gel gives a basis of comparison from one test shot to another. That consistency is its strength. (Do I really need to point out the pun in that statement? Really?)

If you wanted a human flesh simulant, pig carcasses are useful.

It's very difficult to recreate the thinness and toughness of the human body. Dude, we're the friggin' apex of a predatory pyramid. We didn't get here because we're easy to kill. Just sayin'...

Ken

[Michael Emrys]

Dude, we're the friggin' apex of a predatory pyramid.

So far...

:eek:

Michael

[Michael Emrys]

Hyperplasticity happens if the impact is fast enough to cause dispersion of the compression waves generated by the collision in the target material to keep ductile [plastic] deformation modes for greater strains than can be achieved in quasistatic deformations. The exact mechanisms are still being studied, but the dispersion of the medium are clearly the key. Since these are momentum deformations rather than hydrostatic deformations, the Poisson effect does not contribute to changing the yield mode of the material and this allows for ductile, even fluid plasticity to occur much longer.

Gee, that sounds interesting...I wish I understood it. (And don't bother trying to explain it unless your explanation is accompanied by a generous selection of photographs and diagrams.)

Michael

[George MC]

Crews eye view of being hit by AP

[John Kettler]

c3k,

From the Wiki for Ballistic gelatin, it appears we're both partially right.

https://en.wikipedia.org/wiki/Ballistic_gelatin

"Ballistic gelatin is a testing medium scientifically correlated to swine muscle tissue (which in turn is comparable to human muscle tissue), in which the effects of bullet wounds can be simulated. It was developed and improved by Martin Fackler and others in the field of wound ballistics.[1][2][3] Ballistic gelatin is a solution of gelatin powder in water. Ballistic gelatin closely simulates the density and viscosity of human and animal muscle tissue, and is used as a standardized medium for testing the terminal performance of firearms ammunition. While ballistic gelatin does not model the structure of the body, including skin and bones, it works fairly well as an approximation of tissue and provides similar performance for most ballistics testing. Ballistic gelatin is used rather than actual muscle tissue due to the ability to carefully control the properties of the gelatin, which allows consistent and reliable comparison of terminal ballistics."

George MC,

Scale Poligon testing! What will they think of next. Am fascinated by the Tommy driver, who quite clearly lacks the Panzerfeldmutze and other such tank appropriate gear.

Regards,

John Kettler