A question about Chobham/Composite Armor

[pmulcahy11b]

I haven't been able to find an answer to this question (probably due to the classified nature of these armors).

It seems to me that the ceramic/honeycomb matrix part of Chobham would be sort of like a ceramic ballistic plate in Interceptor Body Armor -- it works because the plate spreads out the shock of the round's impact by shattering. You're not dead, but chances are that your ballistic plate is no longer as effective either.

Wouldn't that also happen to Chobham?

[Cdnwolf]

From WIKI

Due to the extreme hardness of the ceramics used, they offer superior resistance against a shaped charge jet and they shatter kinetic energy penetrators (KE-penetrators). The (pulverised) ceramic also strongly abrades any penetrator. Against lighter projectiles the hardness of the tiles causes a "shatter gap" effect: a higher velocity will within a certain velocity range (the "gap") not lead to a deeper penetration but destroy the projectile itself instead.[1] Because the ceramic is so brittle the entrance channel of a shaped charge jet is not smooth — as it would be when penetrating a metal — but ragged, causing extreme asymmetric pressures which disturb the geometry of the jet, on which its penetrative capabilities are critically dependent as its mass is relatively low. This initiates a vicious circle as the disturbed jet causes still greater irregularities in the ceramic, until in the end it is defeated. The newer composites, though tougher, optimise this effect as tiles made with them have a layered internal structure conducive to it, causing "crack deflection".[2] This mechanism using the jet's own energy against it, has caused some to compare the effects of Chobham to those of reactive armour. This should not be confused with the effect used in many laminate armours of any kind: that of sandwiching an inert but soft elastic material such as rubber, between two of the armour plates. The impact of either a shaped charge jet or long-rod penetrator after the first layer has been perforated and while the rubber layer is being penetrated will cause the rubber to deform and expand, so deforming both the back and front plates. Both attack methods will suffer from obstruction to their expected paths, so experiencing a greater thickness of armour than there is nominally, thus lowering penetration. Also for rod penetrations, the transverse force experienced due to the deformation may cause the rod to shatter, bend, or just change its path, again lowering penetration.

[pmulcahy11b]

So, in T2K, we are going to have a lot of composite armor-protected vehicles with compromised armor in many spots. Damn I have a headache...wait, it's a new rule trying to break out of my head...!

[Grimace]

Don't get too much of a headache thinking about a new rule. The area affected as "compromised" would be substantially smaller than a like area of reactive armor.

So the effect of "compromising" the armor wouldn't be any greater than the compromising nature of a round impacting regular armor. It simply weakens the area. So if you could somehow manage to hit the exact same area with another round.... yes, you could do probably significantly better damage. The chances of doing that, though, are pretty small.

[kato13]

Originally Posted by Grimace

It simply weakens the area. So if you could somehow manage to hit the exact same area with another round.... yes, you could do probably significantly better damage. The chances of doing that, though, are pretty small.

You would actually have to hit the same area at a similar angle (when dealing with foot thick armor) so the chances get even smaller.

[pmulcahy11b]

Originally Posted by Grimace

Don't get too much of a headache thinking about a new rule.

No problem -- I took some Vicodin and Skelaxin.

[Abbott Shaull]

Yes I would agree that one would have to hit the place where a hit occurred and the practically the same angle to do real additional damage.

Now what one has to remember is that many of the AFVs have been used for repeated target practice over and over again in 1996, 1997 and 1998 with what ever other engagements they had been in since then with additional damage for additional hits.

I am sure as tank go through more and more engagement the odds increase they will have areas of their armor that aren't as strong as it used to be. It is why some units have turned some of their armor into immobile pillboxes with sandbags, building material, and good old mother earth add more protection leaving only the turret expose for the purpose of being able to engage attackers of their defense.

[Legbreaker]

While there was the oportunity, previously struck plates would be swapped out with those from damaged and destroyed vehicles. As the war dragged on, less and less of these replacement parts are likely to be available.

This could be handled by Wear Factor of the vehicle.

[pmulcahy11b]

Originally Posted by Legbreaker

While there was the oportunity, previously struck plates would be swapped out with those from damaged and destroyed vehicles. As the war dragged on, less and less of these replacement parts are likely to be available.

This could be handled by Wear Factor of the vehicle.

At 24th ID when the neighboring armor unit (5/13 Armor IIRC) got their M-1s, there was a policy about the armor. If, for example in a training accident, the armor was gouged to the point that a red layer was showing, the tank was immediately taken 3rd Echelon maintenance, and unit maintenance was not allowed to fix it. That's an example of how classified Chobham was at the beginning.

[copeab]

Originally Posted by Legbreaker

This could be handled by Wear Factor of the vehicle.

Made-up-on-spot rule:

Whenever a "1" is rolled to-hit against an armored vehicle using a KE round, there is a chance that the round has hit a spot previously hit by another round, reducing the armor protection. Roll d% against the target vehicle's wear value. If the roll is under the wear value, the armor protects at half value (round up). If the wear value is rolled exactly, the armor provides only 1/10 value (round up).

Not particularly realistic (too likely), but simple to use.

[Legbreaker]

I haven't looked in a while, but I seem to remember V1 allows 10 penetrations before that location is no longer protected.
I could also be just remembering vests and helmets...

[Targan]

Originally Posted by Legbreaker

While there was the oportunity, previously struck plates would be swapped out with those from damaged and destroyed vehicles. As the war dragged on, less and less of these replacement parts are likely to be available.

This could be handled by Wear Factor of the vehicle.

As is typical of my group's propensity for making our T2K rules more and more complicated we ended up having multiple wear values on our vehicle sheets. Engine and drive train, optics and electronics, weapon systems, etc. We never did include a separate wear value for armour but having read this thread I'm thinking perhaps we should have.

[General Pain]

Originally Posted by pmulcahy11b

I haven't been able to find an answer to this question (probably due to the classified nature of these armors).

It seems to me that the ceramic/honeycomb matrix part of Chobham would be sort of like a ceramic ballistic plate in Interceptor Body Armor -- it works because the plate spreads out the shock of the round's impact by shattering. You're not dead, but chances are that your ballistic plate is no longer as effective either.

Wouldn't that also happen to Chobham?

Are you asking as a GM,player or designer?

[pmulcahy11b]

Originally Posted by General Pain

Are you asking as a GM,player or designer?

Initially, as a curious individual.

[Dog 6]

All I can say is yes and no, my tank was hit by 125mm boot rounds at less the 500m, all same general area of the turret. the armor was not compromised in any way. it's a steel encased honeycomb, hope that helps.