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Perforated Steel Body Armor


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#1 Burncycle360

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Posted 29 March 2020 - 2217 PM

There has been a race to the bottom with regards to body armor prices, probably due to the rise in popularity of a "prepper" culture rather than a practical need.   Steel and UHMWPE seem to be gaining a lot of traction for their low materials cost, with ceramic lagging behind. 

A lot of these companies are selling products that are not NIJ certified, though will often still reference NIJ standards and have their own rating system.

In addition to their inherent pros and cons (weight, thickness, spalling etc)  steel armor seems to struggle with higher velocity rounds (M193 is a common example) while handling the steel core (M855) okay, while UHMWPE has the opposite problem -- they seem to handle M193 okay but struggle with M855.  Since both of these rounds are readily available off the shelf this is a dealbreaker for many, and companies have responded by thickening the plate despite the weight and coming up with their own ratings, like "Level III+"

As an armored vehicle enthusiast, if I understand correctly, perforated steel armor is used in some armored vehicles, and the hardness, hole size, and hole spacing are generally tuned to ameliorate a particular threat by disrupting it's ability to pass through without experiencing some sort of disruptive shear force?  Would there be any merit to combining UHMWPE with an embedded perforated steel plate "tuned" to defeat M855?  Embedded just inside, the steel plate would be encased and supported in all sides by the UHMWPE preventing chunks from displacing (I presume it would be quite brittle) and also serving as spall protection.  The end result ideally being more like a ceramic plate -- not as thick as UHMWPE alone, not as heavy as steel alone, but not as expensive as Ceramic.

We're not seeing that sort of thing, and I don't know if it's because companies aren't innovating (perhaps they just don't know about the experiments in the armored vehicle world), if the perforated steel armor doesn't scale well from a physics point of view, or some other practical reason (manufacturing, liability, etc)


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#2 Interlinked

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Posted 30 March 2020 - 0104 AM

Well, it will probably work, but it's going to be very bulky.


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#3 KV7

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Posted 30 March 2020 - 0358 AM

Well, it will probably work, but it's going to be very bulky.

Right you are going to need a ~ 50 mm thick array in order to allow for a sufficient space for the core to rotate and a sufficiently thick backing plate. 


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#4 Burncycle360

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Posted 30 March 2020 - 1934 PM

 

Well, it will probably work, but it's going to be very bulky.

Right you are going to need a ~ 50 mm thick array in order to allow for a sufficient space for the core to rotate and a sufficiently thick backing plate. 

 


Would a perforated armor scheme require at least some degree of air-gap then, or can the interstitial space be made up of anything as long as it's less dense than the steel?


Edited by Burncycle360, 30 March 2020 - 1935 PM.

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#5 Interlinked

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Posted 31 March 2020 - 0111 AM

 

Would a perforated armor scheme require at least some degree of air-gap then, or can the interstitial space be made up of anything as long as it's less dense than the steel?

 

 

The ideal design includes an air gap, and indeed, I'd go as far as to say that an air gap is needed for the perforated armour to actually perform according to its operating principle. A low density filler may actually help to stabilize the trajectory of the bullet core, which is totally counterproductive.


Edited by Interlinked, 31 March 2020 - 0111 AM.

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#6 Burncycle360

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Posted 31 March 2020 - 0515 AM

 

 

Would a perforated armor scheme require at least some degree of air-gap then, or can the interstitial space be made up of anything as long as it's less dense than the steel?

 

 

The ideal design includes an air gap, and indeed, I'd go as far as to say that an air gap is needed for the perforated armour to actually perform according to its operating principle. A low density filler may actually help to stabilize the trajectory of the bullet core, which is totally counterproductive.

 


Ah, makes sense thank you


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#7 Paul Lakowski

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Posted 31 March 2020 - 1416 PM

perforated armor works by forcing the projectile to yaw sharply through the plate so when it strikes the main armor its penetration drops sharply.. If the air gap between the main armor and the perforated plate is not large enough , the projectile is supported by both plate and main armor, so it hardly yaws at all. Which is why gap fillers are not good enough. Even a brittle projectile may not shatter in such a case. 

 

If the air gap is wide enough  [LOS] the projectile may hit the main armor sideways and lose most of its potential.

 

Its got to be AFV armor even light AFV.


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#8 KV7

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Posted 02 April 2020 - 0449 AM

Some sort of reactive or low stiffness filler could perhaps work in the cavity, but that will increase TE but not the minimum thickness required for the core to yaw.


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#9 Paul Lakowski

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Posted 03 April 2020 - 1138 AM

With out an gap the projectile will not exaggerate its yaw.  

 

Filler will only slow any rotation of the projectile, thus limiting this yaw. BUT if we are speaking about body protection  its moot point .


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#10 KV7

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Posted 11 April 2020 - 0411 AM

With out an gap the projectile will not exaggerate its yaw.  

 

Filler will only slow any rotation of the projectile, thus limiting this yaw. BUT if we are speaking about body protection  its moot point .

It will depend on the 'filler', as not all of the possible fillers will be able to stabilise the core. E.g. a thin sheet of some ductile material (Dyneema fabric, HHS, UHMWPE will not limit yaw, and may actually accelerate it as it resists the tip. But the ME of such thin elements alone is poor.


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#11 TTK Ciar

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Posted 11 April 2020 - 2150 PM

Coming late to the conversation.  Yeah, what they said.  Body armor usually cannot take advantage of the synergies used in AFV armor because of the limited space budget.  A perforated plate layer + airgap would add too much bulk and people wouldn't wear it.

If I wanted to mass-produce inexpensive SAPI without too much weight or bulk, I would opt for a composite of vinylester filled with unsintered silicon carbide granules, cast in molds lined with HDPE film bags for easy release.  It would be marginally bulkier than Interceptor ESAPI plates and about 20% heavier for a given level of protection, but offer superior multi-hit resistance at a fraction of the manufacturing cost of sintering SiC into whole plates.

I have a journal article somewhere about the impacts of granule size on the composite's physical characteristics, but don't remember offhand the optimal size.  A quick search doesn't bring it up.  I'll link to it here if I find it.


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#12 KV7

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Posted 12 April 2020 - 0052 AM

You would optimally want a mix of particle sizes and considerable compaction in order to to achieve high density. A small amount of UHMWPE fibres might help too (the epoxy or vinyl substrate itself will have not great tensile strength).


Edited by KV7, 12 April 2020 - 0307 AM.

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#13 JWB

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Posted 12 April 2020 - 1108 AM

how much bulk is too much?


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#14 TTK Ciar

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Posted 12 April 2020 - 1454 PM

When people who have body armor leave it behind instead of wearing it, it's too bulky (or heavy, or hot).

I'd love to see a study of thresholds of such, but haven't seen any.


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#15 JWB

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Posted 12 April 2020 - 2004 PM

OK, asking the question in a different way. How wide must the air gap be?

Decades ago I had a pal fire 30/06 FMJ into .1 inch mild steel. I never found what came out the other side. I do know the jacket was stripped because it flew back and hit him in the forehead. The hole in the plate appeared to be about .15 inch in diameter and petaled on both sides. The lead core was obviously "spaghettified" and would do nasty things to flesh and bone. But I doubt it would perforate .25" Al after travelling another 4".


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#16 KV7

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Posted 12 April 2020 - 2321 PM

OK, asking the question in a different way. How wide must the air gap be?

Decades ago I had a pal fire 30/06 FMJ into .1 inch mild steel. I never found what came out the other side. I do know the jacket was stripped because it flew back and hit him in the forehead. The hole in the plate appeared to be about .15 inch in diameter and petaled on both sides. The lead core was obviously "spaghettified" and would do nasty things to flesh and bone. But I doubt it would perforate .25" Al after travelling another 4".

The mechanism of defeat here is not fragmentation of the core and dispersion of the fragments (though fracturing the tip on long rods is possible) - i.e. it is not a Whipple shield, but rather it is inducing a tumbling motion via asymmetric forces encountered in passing the perforated precursor plate(s). Ideally the incoming projectile will hit the perforated plate on one edge of one hole, and then it will be in effect shoved sideways and start tumbling. But the amount of tumbling will not be uniform (it will depend on where the projectile strikes the perforated plate among other things) and so there is no simple corresponding ideal air gap, but generally bigger is better, as it is impossible to get more than 90 degrees of yaw in any sort of reasonable air gap.


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#17 JWB

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Posted 13 April 2020 - 1134 AM

 

OK, asking the question in a different way. How wide must the air gap be?

Decades ago I had a pal fire 30/06 FMJ into .1 inch mild steel. I never found what came out the other side. I do know the jacket was stripped because it flew back and hit him in the forehead. The hole in the plate appeared to be about .15 inch in diameter and petaled on both sides. The lead core was obviously "spaghettified" and would do nasty things to flesh and bone. But I doubt it would perforate .25" Al after travelling another 4".

The mechanism of defeat here is not fragmentation of the core and dispersion of the fragments (though fracturing the tip on long rods is possible) - i.e. it is not a Whipple shield, but rather it is inducing a tumbling motion via asymmetric forces encountered in passing the perforated precursor plate(s). Ideally the incoming projectile will hit the perforated plate on one edge of one hole, and then it will be in effect shoved sideways and start tumbling. But the amount of tumbling will not be uniform (it will depend on where the projectile strikes the perforated plate among other things) and so there is no simple corresponding ideal air gap, but generally bigger is better, as it is impossible to get more than 90 degrees of yaw in any sort of reasonable air gap.

 

This reply doesn't address what I wrote. The defeat mechanism neither fragments the projectile nor causes it to tumble. Rather the outer plate causes so much deformation of the core that perforation of the backing plate becomes impossible.


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#18 KV7

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Posted 13 April 2020 - 1228 PM

Ok it is a semantic issue. I took 'spaghettified' to mean 'FUBAR' aka 'fragmented'  by analogy to 'spaghettification' of matter approaching a black hole, not  'extruded'.


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#19 DB

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Posted 17 April 2020 - 1049 AM

I suspect that if air gaps and perf. plates were workable on personal armour, we'd see them being used. I wonder if that "dragon skin" stuff relied any on edge effects.

Edited by DB, 17 April 2020 - 1050 AM.

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#20 KV7

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Posted 18 April 2020 - 0323 AM

I suspect that if air gaps and perf. plates were workable on personal armour, we'd see them being used. I wonder if that "dragon skin" stuff relied any on edge effects.

As noted above, the modules would be far too bulky. The closest you will get to personal protection where it may be workable is gunshields and ballistic shields.


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