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Here we go, from Armor: Materials Theory and Design:

 

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However, some effort has been made to design a perforated system to protect against APFSDS ammunition, but the results have shown little advantage in doing so (Weber 2002). Nevertheless, if yaw can be induced into the rod, then the depth of penetration into residual armour can be significantly reduced. Even yaw angles as low as 1.5° can result in the degradation of the rod’s performance (Roecker and Grabarek 1986).

This diagram is also included:

UXKv3EX.jpg?1

I am curious about exactly what the author means by "perforated."  Presumably they are talking about a big sheet of armor with holes drilled into it.  But there are many other shapes that could be used to induce yaw in a penetrator; for instance an array of cylinders arranged parallel to the expected threat direction encased in some less dense material.  According to some calculations this is actually more efficient than the traditional perforated sheet, but it is far less convenient to manufacture.

Sadly, Hazell's book does not contain any information on the use of uranium in armor.

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I would have thought that if the projectile tended to normalise then something like this would be ideal:

FnPpLNa.jpg

The black stripes are simpy sheets of armour plate, with the white stripes being spacers or air gaps. The projectile then tends to normalise away from the array as it goes - presumably popping out of the top of the array in some cases.

I have no idea what a shaped charge does in this situation though.

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While looking for information on perforated armour, I bumped into this:

http://www.abovetopsecret.com/forum/thread162738/pg1

 

This shit is why it's so disappointing to discover that all the secret armour out there is essentially NERA. Look at the description of chobham: layers of high-hardness steel and advanced ceramics! With kevlar fibre-reinforced back plates! And a strike face of ultra-hard, ultra-tough DU/tungsten alloy! It all sounds so space-age and high tech - the penetrators just bouncing off this magic stuff as the crew no doubt hangs out of the hatches, laughing maniacally.

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1 hour ago, Toxn said:

I would have thought that if the projectile tended to normalise then something like this would be ideal:

FnPpLNa.jpg

The black stripes are simpy sheets of armour plate, with the white stripes being spacers or air gaps. The projectile then tends to normalise away from the array as it goes - presumably popping out of the top of the array in some cases.

I have no idea what a shaped charge does in this situation though.

A while ago I came up with something like this:

Jhussu5.png

As long as you keep that pointed at the enemy it should be the most effective armour.

 

If you can actually make it.

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Wouldn't it be better to just have the top half of the array? This would be easier to make and would still work fine for deflecting any projectiles coming in from the horizontal or above. I don't think you get hit by too many penetrators from below.

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1 minute ago, Toxn said:

Wouldn't it be better to just have the top half of the array? This would be easier to make and would still work fine for deflecting any projectiles coming in from the horizontal or above. I don't think you get hit by too many penetrators from below.

Colli and I were talking about how you want to keep your hull horizontal to prevent long rod penetrators from hitting your roofs. This design is assuming the same: no attacks from a non-horizontal angle. You should be fine if you get a hit from above though (as long as they don't hit the top bit). Plates are angled at 5 degrees, but if you get a hit parallel to the plates, they more or less serve as thick perforated armour. 

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I am still very sceptical about the Abrams using perforated DU armor; there is no trustworthy source. It started as a speculation (remember Chobham armor being the "honeycomb-shaped ceramic armor matrix") that has been repeated over and over again.

 

The diagram shows that jaw can be extremely effective at reducing the penetration power of APFSDS ammunition; however sloped ERA and NERA plates also induce jaw at a penetrator, while also having other advantageous defeat mechanism. DU being used as purely passive armor type shoudln't lead to a very high mass efficiency.

 

35 minutes ago, Bronezhilet said:

As long as you keep that pointed at the enemy it should be the most effective armour.

 

If you can actually make it.

 

Which will never happen thanks to trajectory and uneven ground :D

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So, comparing DU, Steel and Titanium penetration values here, I get the following results for vertical impacts against the standard tungsten dart:

  • Mild steel (150 BHn): 720mm
  • Armour plate (300 BHn): 574mm 
  • High carbon steel (500 BHn): 534mm
  • Ti-6Al-4V titanium alloy (solution heat treated and aged to 315 BHn): 749mm
  • Staballoy (age hardened to 450 BHn): 340mm
  • 7075 T651 aluminium alloy (heat treated and aged to 150 BHn): 1207mm

Unfortunately the calculator can't handle hardnesses below 150 BHn or about 500 BHn, so a lot of territory is missing. Even so, we can see that Titanium alloy is about 2 times as good as armour plate on a per-weight basis, DU is about 4 times worse and your hardest aluminium alloy is an amazing 6 times better. As such; my feeling is that either something is wrong with the penetration model, or NERA with an aluminium flyer plate should be an amazing idea given the effectiveness per weight.

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On 2/8/2017 at 10:15 AM, SH_MM said:

I have seen these rumors about "a DU mesh" acting like perforated armor at other places. However it was always either Wikipedia (without mentioning a source) or another website/forum quoting Wikipedia. There seems to be no reputable source describing the DU armor in the Abrams' turret as mesh or perforated plate.

DU supposedly has a higher ME against shaped charges than steel (old source on tank-net, unfortunately Google blocks access due to phishing claims).

You can bypass the warning page.

I would be surprised if DU has higher ME against shaped charges than steel, since ME against shaped charges can be roughly plotted as an inverse function of density (see Ogorkiewicz).  And that applies to things that aren't even metals, like fuel, water and plastic.  I realize that actinides have strange physical properties, but I don't think they're that strange.

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Toxn,

It's pretty funny seeing a link to that site dropped here, especially with the posters who were involved in this thread!

 

The poster ch1446 in another thread on the same site came up with an idea for an unmanned/autonomous weapons system that, at the time, was not feasible but every year since the year when it was posted brings it oh so much closer....

I really hope it's a system that never gets built though, because it would almost certainly bring about an era where any asshole with an ali express account and a black MasterCard could order a literal brutal totalitarian regime starter kit sufficient to dominate a smaller city that flat packs into a single 40 foot shipping container...

*shudders* Anyway though, yeah that very much WAS at one point a very interesting place to hang out online!

 

 

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20 hours ago, roguetechie said:

The poster ch1446 in another thread on the same site came up with an idea for an unmanned/autonomous weapons system that, at the time, was not feasible but every year since the year when it was posted brings it oh so much closer....

I really hope it's a system that never gets built though, because it would almost certainly bring about an era where any asshole with an ali express account and a black MasterCard could order a literal brutal totalitarian regime starter kit sufficient to dominate a smaller city that flat packs into a single 40 foot shipping container...

*shudders* Anyway though, yeah that very much WAS at one point a very interesting place to hang out online!

Dubious

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On 2/10/2017 at 10:13 AM, Toxn said:

My my... it seems you've found a pretty recent RAFAEL patent on the NxRA. Could be Merkava-related. I'll be sure to save it. 

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On 2016/10/29 at 5:33 PM, Militarysta said:

And here older version, from Type.85-II and 85-III and very very erly Type-96:

 

i1kwEQh.png

 

From here:

 

NwW4S44.jpg

 

And Type 85 erly armour:

 

Vkinlhi.jpg

 

y6Fi5gy.jpg

 

XUoXB2e.jpg

 

 

To be honest - I would like sitting in old T-72B (Ob.184) then in those chineese tanks above - those armour modules have huge weak zones couse it's NERA placment inside...

As I understend - this was relesed to public in china so in Type-96A and newest tanks there must be completly diffrent armour configuration.

 

And you are right about this.

The tank in your picture is Type85 tank, its armor is just about the same level as T-72M1 (no kidding), so T-72B do has much better protection.

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On ‎13‎/‎02‎/‎2017 at 11:30 AM, Toxn said:

The first paper demonstrates that target hardness has an effect on shaped charge penetration, while the second paper argues very convincingly that there is an optimal target density for a given charge configuration. High-hardness titanium alloys just so happen to slide perfectly into both mechanisms, with glass being a little on the light side but close enough to have greater-than-expected efficiency. Alumina should also work well here. Steel armour, interestingly enough, should only become optimally efficient once the jet velocities get really high.

 

This, I think, also provides a good explanation for why aluminium armour isn't that good against shaped charges - it's too soft and too light to fall within the butter zone.

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With all of the above, we finally have a formula for why NERA is so prolific:

 

The basic issue is long rods and shaped charges penetrate, to a first approximation, in proportion to their length. Accordingly, the first order of business is to deform or break up the penetrator. This is why NERA and ERA are so good - because only reactive armours can even attempt to do this. It also helps that, as a byproduct of moving towards the penetrator, the reactive armour will tend to feed material into it and effectively increase the volume of material that the penetrator has to plough through.

This does not mean, however, that material properties are useless beyond mere density - high hardness can provide a 30-40% improvement in TE at 'lower' velocities (ie: sub-3km/s). Even where density is concerned, there are optima to be found which can increase ME and TE significantly.

 

So here, then, is the recipe for NERA - an array of modules arranged at a significant angle to the penetrator, the modules being composed of two plates seperated by an incompressible solid (or a liquid, if you can find a way to keep it from leaking). The penetrator, striking the module, forces the plates away from each other due to the action of the incompressible middle layer. Both, in deforming, will tend to feed material into the path of the penetrator, with the facing plate potentially applying a shearing force to the penetrator as well. Finally; where long rods are concerned the rod will tend to bend towards the module during penetration - something which may be less pronounced where the rod is more rigid.

As to the materials and exact composition: equally-sized RHA plates seperated by rubber will do (rubber being the solid which comes closest to being incompressible), but my guess is that unevenly-sized plates would provide an advantage in terms of optimising their function. Here my guess is a lighter (thinner) facing plate and heavier (thicker) backing plate, as this will tend to maximise the shear forces applied. While doing so, the best approach might also be to use a high-hardness titanium facing plate in order to get the highest mass efficiency and plate velocity.

Further improvements might be to put a thin skin of high-density material in front of the modules, to eat up the highest-velocity portions of a shaped charge tip. A ceramic sandwich array might also be a good option. Behind the array, it might be a good idea to have a high mass-efficiency plate (possibly a high-hardness aluminium alloy) to deal with residual penetration. This, in turn, might be backed by a final layer of RHA to provide structural support and a last, high-ME barrier. The whole arrangement; modules, front and back plates etc; should ideally be enclosed in an armoured box for ease of repair and replacement.

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2 hours ago, Toxn said:

-snip-

So I practice, this?:
7FBhg8n.png

Black=Steel
Brown=Rubber
Grey=Titanium
Light blue=Aluminum
Orange=Ceramics

 

To explain:
First the penetrator hits the spaced angled ceramic armor, then flies through a airspace and maybe tumbles and curves into the plate, then it hits the NERA array and curves upwards because of the reverse angling of the plates, breaks up. Then the rest is absorbed by the high hardness aluminum layer, before being completely stopped by the ceramic layer. 

The spaced High hardness plate should cause the penerator to turn into the plate, increasing the LOS thickness of the rest of the array, then again, when hitting the reverse slope of the NERA array, it should curve upwards, increasing the LOS thickness again.

 

(Note, proportions are not right, just a rough sketch) 

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18 hours ago, Xoon said:

So I practice, this?:
7FBhg8n.png

Black=Steel
Brown=Rubber
Grey=Titanium
Light blue=Aluminum
Orange=Ceramics

 

To explain:
First the penetrator hits the spaced angled ceramic armor, then flies through a airspace and maybe tumbles and curves into the plate, then it hits the NERA array and curves upwards because of the reverse angling of the plates, breaks up. Then the rest is absorbed by the high hardness aluminum layer, before being completely stopped by the ceramic layer. 

The spaced High hardness plate should cause the penerator to turn into the plate, increasing the LOS thickness of the rest of the array, then again, when hitting the reverse slope of the NERA array, it should curve upwards, increasing the LOS thickness again.

 

(Note, proportions are not right, just a rough sketch) 

Pretty much, although keep in mind that the ceramic front layer would be quite limted in terms of the geometries and thicknesses you could use. The back ceramic layer is probably also not necessary, given that ceramics seem to work best at high velocities and the function of the back layer is to catch residual penetration and low-velocity fragments.

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A few more thoughts gathered upon reflection:

1.

It seems that one of the problems with getting too clever with your armour arrays is the three-way tradeoff between thickness efficiency, mass efficiency and cost efficiency. It's pretty easy to come up with a wonderfully mass-efficient armour array which is hella thick and costs an obscene amount. This is, I suspect, one of the reasons why the good stuff (staballoy, titanium etc) only shows up in tryhard turret front arrays.

 

2.

Another problem is that these sorts of arrays may be very sensitive to changes in angle of impact. For instance; the normalising array I was considering (which Xoon has helpfully drawn as well) starts to look very silly once projectiles begin to arc down at angles greater than about 30' or so. One fix for this might be to reverse the direction of the array:

E8pA4fA.jpg

Blue - crew compartment

Grey - RHA

Yellow - high-hardness aluminium alloy

Light blue - titanium

Black - rubber

Purple - staballoy

 

This would be more useful against top attack munitions and missiles arcing down from on high, but would tend to direct long rods downwards. So it might need a fat bottom plate to catch the residual penetration.

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Could this design work? 

63lE2fN.png

Grey - Steel
Grey stripes - NERA plates at a reverse slope of 30 degrees from horizontal. 
Orange - Shatter layer, either Ceramic or Tu/DU/Staballoy. 
Yellow - Ceramics for high ME and to shatter the penertator.
Light blue - Backplate, steel, titanium or high hardness aluminum alloy.

 

In this layout, a top attack coming in at 30 degrees would hit the NERA plates at 30 degrees. A straight on attack would also hit the plates at 30 degrees. The entire array is sloped backwards to take advantage of the normalization effect. 
 

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On 14.02.2017 at 1:28 PM, Toxn said:

With all of the above, we finally have a formula for why NERA is so prolific:

 

The basic issue is long rods and shaped charges penetrate, to a first approximation, in proportion to their length. Accordingly, the first order of business is to deform or break up the penetrator. This is why NERA and ERA are so good - because only reactive armours can even attempt to do this. It also helps that, as a byproduct of moving towards the penetrator, the reactive armour will tend to feed material into it and effectively increase the volume of material that the penetrator has to plough through.

This does not mean, however, that material properties are useless beyond mere density - high hardness can provide a 30-40% improvement in TE at 'lower' velocities (ie: sub-3km/s). Even where density is concerned, there are optima to be found which can increase ME and TE significantly.

 

So here, then, is the recipe for NERA - an array of modules arranged at a significant angle to the penetrator, the modules being composed of two plates seperated by an incompressible solid (or a liquid, if you can find a way to keep it from leaking). The penetrator, striking the module, forces the plates away from each other due to the action of the incompressible middle layer. Both, in deforming, will tend to feed material into the path of the penetrator, with the facing plate potentially applying a shearing force to the penetrator as well. Finally; where long rods are concerned the rod will tend to bend towards the module during penetration - something which may be less pronounced where the rod is more rigid.

As to the materials and exact composition: equally-sized RHA plates seperated by rubber will do (rubber being the solid which comes closest to being incompressible), but my guess is that unevenly-sized plates would provide an advantage in terms of optimising their function. Here my guess is a lighter (thinner) facing plate and heavier (thicker) backing plate, as this will tend to maximise the shear forces applied. While doing so, the best approach might also be to use a high-hardness titanium facing plate in order to get the highest mass efficiency and plate velocity.

Further improvements might be to put a thin skin of high-density material in front of the modules, to eat up the highest-velocity portions of a shaped charge tip. A ceramic sandwich array might also be a good option. Behind the array, it might be a good idea to have a high mass-efficiency plate (possibly a high-hardness aluminium alloy) to deal with residual penetration. This, in turn, might be backed by a final layer of RHA to provide structural support and a last, high-ME barrier. The whole arrangement; modules, front and back plates etc; should ideally be enclosed in an armoured box for ease of repair and replacement.

You should pay attention to T-80U armor (at least turret armor) that have "pockets" full of quasi-liquid material. It is one of not many MBTs that have non-NERA armor (at least in turret).

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