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Author: Subject: [Metalurgy] Homemade steel body armor
AJKOER
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[*] posted on 1-2-2018 at 08:56


Quote: Originally posted by clearly_not_atara  
The problem with a bag of rocks is that it's too heavy to move in. You could achieve better protection by simply, I don't know, standing inside of a building. It does stop the bullet, because the bullet has to hit a specific pebble, and so about 50% of its kinetic energy will be transferred to this pebble, likely traveling in an oblique direction towards other pebbles, while the bullet ricochets towards the other pebbles. But such a suit would weigh 1m tall * 5 dm wide * 5 cm thick * 5 kg/L -> 125 kg! Good luck moving with 125 kg of rocks on your back, and those are generous numbers.....

...For more practical purposes, there's an interesting alumina-PMMA composite which imitates seashells:

"Recently, synthetic, yet bioinspired, bulk ceramic materials havebeen made in the image of the nacre structure 25 . Using alumina ceramic powders mixed with water and frozen using a freeze-casting (ice-templating) technique 25,26 , ceramic scaffolds can be processed with layer thicknesses (of ~1–100 μm) controlled by the rate of cooling, and interlayer roughnesses controlled in part by the addition of dopants (sugar, salt or alcohol). After cold pressing and infiltrating with a polymeric lubricant phase (poly(methyl methacrylate), PMMA), ‘brick-and-mortar’ 85 vol.% alumina ceramic–PMMA hybrid materials have been made in bulk form in the image of nacre (Fig. 5b). The resulting mechanical properties of these bioinspired ceramics are nothing short of remarkable, with strengths comparable to pure alumina but fracture toughnesses an order of magnitude larger (Fig. 5c). Indeed, toughness values can exceed 30 MPa m 1/2 (Fig. 5d) making these materials the highest toughness ceramics on record 25 ."
........


Vow, is part of your comment actually supportive of sea-shell armor:o?

Yes, I agree weight can be and has historically has been an issue for armor. Take your average heavy plated tank, which continues to face advances in armor piercing projectiles (I did noticed this issues is conveniently omitted when discussing armor platting vests).

Interestingly, one answer to the tank armor issue has not been more metal (increases weight, cost and slows the vehicle and reduces its range of operation), or harder materials (much higher cost). One solution in practice is deflecting projectiles with a layer of reactive armor (see https://en.wikipedia.org/wiki/Reactive_armour ).

So, if the seashell vest is too heavy, theoretically think of redesigning so that a thinner vest has an outer layer consisting of a type of personal reactive armor. One comment on the latter, to quote cyberdude78 (link: http://www.abovetopsecret.com/forum/thread131300/pg1):

"I figure the only practical idea at this point for reactive armor is the one that works on the corn starch concept. Basically it's liquid in a bag normally, but a high velocity object causes it to harden nearly instantly."

So, if I make this personal armor and I am asked how it works, the honest answer is seashells with a skin of reactive armor based the corn starch concept.

Any volunteers for testing?
---------------------------------------

On a more serious note, the ability of the common man to construct effective low cost protective armor may be a game changer for those who would rule by force of arms alone.

[Edited on 1-2-2018 by AJKOER]
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[*] posted on 1-2-2018 at 20:57


Quote: Originally posted by Fulmen  
As most patterns will end up crossing the edge both alloys need to have similar mechanical properties to retain a useful cutting edge.


When it comes to holding an edge, modern steel is better than damascus for that reason. But if a cutting edge is not required, the alloys can have very different properties. There are a lot more intact 400 year-old katanas sitting around than there are unbroken 150 year-old sabres.





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[*] posted on 1-2-2018 at 21:54


Nice to finally see some people getting interested in such full of potential subject.

Quote: Originally posted by Fulmen  
Ajoker: A bag of rocks will be better than nothing, but it won't be uniform in thickness/resistance. And what prevents the rocks from moving out of the way of the projectile? Another important function of ballistic armor is to spread the impact out over a larger area, I don't see how your idea would accomplish this. As for fragments, remember that this will occur a few inches below your face, so the risk of you being hurt by this would be greater than the risk to the shooter.

JJay: Why? As far as I understand, damascus steel can mean two things. The first is blades made from Wootz steel, a legendary Indian steel that contained certain beneficial alloying elements. The second is any patterned steel made by two or more distinct alloys. Neither has any properties that would rival modern steel.

A good choice would be a low alloy steel, for instance a chromium/molybdenum/manganese steel with a low/medium carbon content. These can be heat treated to fairly high strength while retaining excellent impact resistance.

The real challenge of any steel armor would be weight. I have a Lv4 composite ceramic insert lying around, it is appr. 260x300mm, 18mm thick. It weighs 3.5kg (density appr. 2.5g/cm^3). It's rated for a 166grs 30-06 armor piercing round, which is pretty darn impressive. A steel plate of the same weight would be less than 6mm thick, and I doubt there's a steel available that would stop even a regular .30 FMJ at that thickness.


Precisely. High Strength/Low Alloy (HSLA) steels are generally used in armor plates.
5160 and 9250 get very close to this kind of alloy, but not exactly.
Changing the chemical composition just a tiny bit could result in a high impact on the physical properties of the steel alloy.
The reason why I chose 5160 to make my own body armor is because there are commercially-available personal body armor that are made from T2 and T1, which are closely related to 5160 in some alloys. http://www.matweb.com/search/datasheet.aspx?MatGUID=2163c184...
It was nothing sure to begin with, and the only thing I would be able to do was to test it.
But there are things to consider when choosing the proper steel alloy to use, such as the alloys themselves used and also in which amount they are present in the steel. I detailed some of this part on my original message.

This website provides a more in-depth description on what regular alloys would impact the physical properties of steel.
http://www.otaisteel.com/technical-support/effects-of-common...

Regarding the ceramic body armor, its most likely made out of boron carbide, which was "welded" together by high pressure and vibrations (I don't recall the correct industrial term). It is indeed very lightweight, but lacks the ability of sustaining multiple hits.
If unfortunately somebody hits you with 2 rifle rounds and these rounds impact your body armor too close to each other, there is a very high chance that the last one will go through. The first round would just make way for the second one.
From videos that I have seen on youtube, the crater sized created by a 308 round impacting ceramics body armor is usually 1 to 1.5 inch wide, and I have also seen people shooting smaller groups than 1.5 inches at close range.
I'm just saying that there is a small chance of facing a madman with a rifle and proper training. But I also agree that its a trade off because a boron carbide plate will be much lighter and comfortable than carrying 15 lbs of steel + a gun and extra mags for hours.
I also agree that a steel this thick (1/4") wouldn't stop an armor-piercing 30-06. Maybe a regular FMJ. AR500 channel already tested their level 3+ (maybe 550 or 600 HB) against M2AP. https://www.youtube.com/watch?v=rzmwnU-LdAM

I don't know how much it would cost me, but I could send a plate to somebody from SM and have him test it against different rifle threats that I wasn't able to test against the plate myself.
I can assure that it is at least level 3a rated.

Regarding where I got my steel from, I bought it on the internet from a guy that gets it directly from the industry. The steel was never used before and went through 3 normalizing cycles and then was quenched in warm vegetable oil, and also tempered to the desired hardness.

Here is the TTT for 5160 steel alloy.

5160ttt.jpg - 147kB

[Edited on 2/2/18 by joseph6355]




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[*] posted on 2-2-2018 at 01:17


5160 seems like a decent choice of material. I haven't studied HSLA much, they are a bit murky as they are made to conform to certain physical characteristics rather than a fixed chemical composition. They seem to provide good performance at low cost, but there are far stronger steels out there.





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[*] posted on 2-2-2018 at 03:26


Quote: Originally posted by Fulmen  
5160 seems like a decent choice of material. I haven't studied HSLA much, they are a bit murky as they are made to conform to certain physical characteristics rather than a fixed chemical composition. They seem to provide good performance at low cost, but there are far stronger steels out there.


Definitely. AR500.com utilizes a proprietary steel alloy, which they didn't do a very good job to hide from the public and other companies, at least not fully. They accidentally showed it in a test video of theirs. I'm looking for it and I will link it here once I find it.

Of course, if I were so inclined to do so, I could buy ar600 directly from the manufacturer, but that definitely defeats the purpose of everything.
http://www.alibaba.com/product-detail/alibaba-ar400-ar500-ar...
http://www.alibaba.com/product-detail/AR500-AR600-abrasion-r...
http://www.alibaba.com/product-detail/ar600-hot-rolled-high-...
As you can see, the steel is advertised as low carbon, but also high strength.
There are different chemical compositions. As I said, ARx00 is an industrial nomenclature for certain physical properties that a steel alloy has.
One interesting thing though is that a key alloy that all of them seem to have is Manganese, always in quantities higher than 1% Manganese not only increases the ease of hardening and final hardness to the low carbon steel alloy, but also adds strength to it.
Imagine hardening a AISI 1095 simple carbon steel to 58 HRC. I bet (and guess by experience) that it would be a brittle plate.

chemical composition.png - 16kB

[Edited on 2/2/18 by joseph6355]




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[*] posted on 2-2-2018 at 05:53


I'm guessing AR stands for Abrasion Resistance, the number is the hardness in Brinell. Around here it's sold under the Hardox-brand and is widely used for steel targets. I've never seen anyone recommend anything under 8-10mm for rifle targets, but they are of course intended for sustained use. So it's possible that 6mm of AR5/600 would stop a couple of standard .30 FMJ.

Manganese is probably the second most widely used alloying element after carbon. In addition to it's effect on hardenability it's a good deoxidizer, I believe it also strengthens the ferritic phase.




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[*] posted on 2-2-2018 at 16:58


Quote: Originally posted by Fulmen  
I've never seen anyone recommend anything under 8-10mm for rifle targets, but they are of course intended for sustained use. So it's possible that 6mm of AR5/600 would stop a couple of standard .30 FMJ.

AR600 plates from spartan armor uses .210 thick steel to stop a 3200 ft/s projectiles.
You're very correct. The reason why thicker plates are used is because of the backface deformation. For what I have seen, 1/4" thick plates will deform on the back at the point of impact. The ar500 armor channel measured the depth of this deformation, its approximately 2 mm deep. With 3/8" thick plates, this wouldn't occur.

They also use 1/4" thick plates for pistol targets, but they will withstand rifle calibers with no problem.
https://www.youtube.com/watch?v=nloU9dY0T8c
This guy seems surprised about the fact that it works. But I should note that he shot it 200 yards away with the 5.56 and 308, and 300 yards with the 30-06.
Its common for people to back up a bit. Even though steel targets should be angled downwards at a slight angle, you never know when fragments can go back and hit you.

.50 BMG API vs 1" thick plate.
https://www.youtube.com/watch?v=11BAEBAC3Zg

.50 BMG FMJ vs 1/2" thick plate
https://www.youtube.com/watch?v=vJdz8iVUtiw
Not pass through on both of them.
I suspect that a 3/8" thick plate would stop a .50 BMG FMJ. But I'm just guessing.




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[*] posted on 3-2-2018 at 05:30


As a sidebar to conventional 'steel' body armor, apparently liquid armor has arrived! Some quotes from a 2015 news report:

"Struszczyk said the liquid's stopping capability, combined with the lower indentation of its surface, provides a higher safety level for the user compared with traditional, mostly Kevlar-based, solutions.".....

'If a protective vest is fitted to the body, then a four centimeter deep deflection may cause injury to the sternum, sternum fracture, myocardial infarction, lethal damage to the spleen,' Struszczyk said.

'Thanks to the properties of the liquid, thanks to the proper formation of the insert, we eliminate one hundred percent of this threat because we have reduced the deflection from four centimeters to one centimeter.'
.......
When hit by a high-speed projectile, a wide area of the STF hardens instantly, causing the usually massive energy to be dispersed away from the wearer's internal organs.

Implementing the solution in body armor required designing special inserts, but the company says those are lighter than standard ballistic inserts and broader range of movement for their users in the police and military.

'The point is for them not to interfere, not change the way of movement, operation of such the product by the user, and at the same time increase their motor skills, increase effectiveness of their decision process and increase their possibilities during the mission at hand,' Struszczyk said."

See video at: http://www.dailymail.co.uk/sciencetech/article-3023905/The-m...

Note, the above comments on liquid armor are a supposed comparison to Kevlar based armor. Comments by Wikipedia (https://en.wikipedia.org/wiki/Kevlar) on Kevlar in relationship to steel:

"Currently, Kevlar has many applications, ranging from bicycle tires and racing sails to bulletproof vests, because of its high tensile strength-to-weight ratio; by this measure it is 5 times stronger than steel.[2]"

Also, per Wikipedia (https://en.wikipedia.org/wiki/Bulletproof_vest):

"While a vest can prevent bullet penetration, the vest and wearer still absorb the bullet's impulse. Even without penetration, heavy bullets deal enough force to cause blunt force trauma under the impact point."

My conclusion is that liquid armor compared to steel products, given that steel is apparently much weaker in tensile strength that even Kelvar, and that steel plates likely demonstrate a lower dispersion of the kinetic energy of the projectile relative to Kelvar, detailed above as potentially dangerous, makes this an easy choice.

Downside on the liquid armor product, the precise formula is not disclosed, but someone on this forum may provide some good guesses as to compositions for testing. Note, just starch and water, by itself, is not effective enough to stop bullets! See, for example, https://www.youtube.com/watch?v=kK-Ob_dichQ .

[Edited on 3-2-2018 by AJKOER]
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[*] posted on 3-2-2018 at 11:21


The 'precise formula' isn't all that precise, actually. All you need is a mixture of polyethylene glycol (PEG) with a high enough MW for it to be a liquid, and fumed silica. Mix until shear-thickening effect is obtained (usually something like 50-55 vol.%). I'll see if I can dig up the old papers I used to have back when I was trying to make this stuff.



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[*] posted on 3-2-2018 at 13:49


ElementCollector1:

Fantastic!

You have restored my faith on the breadth of talent on this forum!

Here is a link detailing some of ElementCollector1 comment, see https://science.howstuffworks.com/liquid-body-armor1.htm .

I would like to state that I am aware that my comments for a thread on 'steel' body armor may be off-topic. As such, perhaps posting my comments and your work in a new thread on liquid armor may be more appropriate, under General Chemistry, perhaps.

[Edited on 3-2-2018 by AJKOER]
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[*] posted on 3-2-2018 at 14:21


I would be surprised if shear thickening fluids alone would work. But in combination with a more traditional soft armor it could be perfect. As pointed out, the problem with soft armor is that they are soft, limiting how much the can disperse the impact. Adding a STF would allow it to spread out the impact far better without resisting movement.



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[*] posted on 3-2-2018 at 17:29


Quote: Originally posted by Fulmen  
I would be surprised if shear thickening fluids alone would work. But in combination with a more traditional soft armor it could be perfect. ...


My last reference on liquid armor notes a weakness (major?), which is also true for Kevlar. Namely, slow moving objects (like swords, knives, spears,..) can apparently pass through the armor (this may be good news if it results in a total return to ancient warfare, otherwise, no).

So a liquid armor + Kelvar is not quite 'perfect'.
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[*] posted on 3-2-2018 at 22:04


Quote: Originally posted by AJKOER  
As a sidebar to conventional 'steel' body armor, apparently liquid armor has arrived! Some quotes from a 2015 news report:

"Struszczyk said the liquid's stopping capability, combined with the lower indentation of its surface, provides a higher safety level for the user compared with traditional, mostly Kevlar-based, solutions.".....

'If a protective vest is fitted to the body, then a four centimeter deep deflection may cause injury to the sternum, sternum fracture, myocardial infarction, lethal damage to the spleen,' Struszczyk said.

'Thanks to the properties of the liquid, thanks to the proper formation of the insert, we eliminate one hundred percent of this threat because we have reduced the deflection from four centimeters to one centimeter.'
.......
When hit by a high-speed projectile, a wide area of the STF hardens instantly, causing the usually massive energy to be dispersed away from the wearer's internal organs.

Implementing the solution in body armor required designing special inserts, but the company says those are lighter than standard ballistic inserts and broader range of movement for their users in the police and military.

'The point is for them not to interfere, not change the way of movement, operation of such the product by the user, and at the same time increase their motor skills, increase effectiveness of their decision process and increase their possibilities during the mission at hand,' Struszczyk said."

See video at: http://www.dailymail.co.uk/sciencetech/article-3023905/The-m...

Note, the above comments on liquid armor are a supposed comparison to Kevlar based armor. Comments by Wikipedia (https://en.wikipedia.org/wiki/Kevlar) on Kevlar in relationship to steel:

"Currently, Kevlar has many applications, ranging from bicycle tires and racing sails to bulletproof vests, because of its high tensile strength-to-weight ratio; by this measure it is 5 times stronger than steel.[2]"

Also, per Wikipedia (https://en.wikipedia.org/wiki/Bulletproof_vest):

"While a vest can prevent bullet penetration, the vest and wearer still absorb the bullet's impulse. Even without penetration, heavy bullets deal enough force to cause blunt force trauma under the impact point."

My conclusion is that liquid armor compared to steel products, given that steel is apparently much weaker in tensile strength that even Kelvar, and that steel plates likely demonstrate a lower dispersion of the kinetic energy of the projectile relative to Kelvar, detailed above as potentially dangerous, makes this an easy choice.

Downside on the liquid armor product, the precise formula is not disclosed, but someone on this forum may provide some good guesses as to compositions for testing. Note, just starch and water, by itself, is not effective enough to stop bullets! See, for example, https://www.youtube.com/watch?v=kK-Ob_dichQ .

[Edited on 3-2-2018 by AJKOER]

It seems very interesting this kind of fluid. I wonder if its good only for pistol calibers or also for rifle ones.

Quote: Originally posted by elementcollector1  
The 'precise formula' isn't all that precise, actually. All you need is a mixture of polyethylene glycol (PEG) with a high enough MW for it to be a liquid, and fumed silica. Mix until shear-thickening effect is obtained (usually something like 50-55 vol.%). I'll see if I can dig up the old papers I used to have back when I was trying to make this stuff.

Nice. I found PEG for sale on the internet, and its fairly cheap, coming for 15 to 30 USD for a pound, depending on the mw I presume.
They are advertised as PEG 1500, 4000, 6000 and 8000. I have no idea what it means.
I cant seem to find fumed silica. I could try to synthesize it, is it too complex or expensive to do so?
Thanks for participating and providing us with details on this amazing new technology. :)




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[*] posted on 3-2-2018 at 22:10


Quote: Originally posted by Fulmen  
I would be surprised if shear thickening fluids alone would work. But in combination with a more traditional soft armor it could be perfect. As pointed out, the problem with soft armor is that they are soft, limiting how much the can disperse the impact. Adding a STF would allow it to spread out the impact far better without resisting movement.

Trauma pads are also sold sometimes in a combo with the kevlar body armor. Some of them are made from other fibers, others are even made from metal, like aluminum.

I think that the main problem with shear-thickening fluids is coming up with an efficient method of containing the fluid inside the vest after it gets perforated by a projectile. Can you imagine getting shot and your body armor leaking all over you and leaving you vulnerable?
We need a flexible material that will sort of repair itself after being perforated, or at least spring back to its original form and compress the hole left by the projectile, and consequently not allowing any of the fluid to escape.
I imagine that we don't need to invent any of this, but how expensive would this material be for the amateur dude that will make this at home and pay everything from his pocket?

[Edited on 4/2/18 by joseph6355]




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[*] posted on 3-2-2018 at 22:45


Quote: Originally posted by joseph6355  

Nice. I found PEG for sale on the internet, and its fairly cheap, coming for 15 to 30 USD for a pound, depending on the mw I presume.
They are advertised as PEG 1500, 4000, 6000 and 8000. I have no idea what it means.
I cant seem to find fumed silica. I could try to synthesize it, is it too complex or expensive to do so?
Thanks for participating and providing us with details on this amazing new technology. :)


Found some more literature on PEG/FS-based shear thickening fluids:

http://iopscience.iop.org/article/10.1088/0964-1726/23/3/035...

https://dspace.mit.edu/handle/1721.1/33904

Fumed silica is usually found in auto shops as a thickener for fiberglass resin or other liquid compounds. I got a decent amount on Ebay cheaply, way back when (2 years ago, actually. : P). Keep in mind that it's sold by volume, so a gallon barely weighs anything!

If you do work with fumed silica, make sure to have respiratory equipment (even a dust mask would be better than nothing) - that stuff's nasty inside your lungs!

https://www.ebay.com/itm/Cabosil-fumed-silica-Gallon/2530768...

According to the Wikipedia page for PEG, the numbers refer to the average molecular weight. I'm not sure where the cutoff is between liquid PEG and solid PEG in terms of molecular weight, but lower is (probably?) better. MW 400 is a liquid, judging from the pictures on websites where you can buy it, but 1500 might be a solid.

Personally, I'm a bigger fan of UHWMPE armor. It's hard to machine in bulk, expensive, and very weak to heat, but it's just about bulletproof at any thickness higher than 1/4" and 7 times lighter than steel. It can also be spun into a fiber (Spectra armor is composed of UHMWPE fabric, that may or may not be mixed with a resin depending on whether it is 'hard' or 'soft' armor). It's definitely better than Kevlar for impact resistance (though definitely not for heat resistance, as mentioned above).

Per your comment on self-healing materials, there aren't many on the market just yet - it's a fairly new technology and still mostly in R&D. One thing I will note is that most kinds of silicone are self-healing... if you heat them to 90 degrees Celsius in an oven for 24 hours and press the broken parts together.

https://www.theengineer.co.uk/issues/january-2012-online/sci...

[Edited on 2/4/2018 by elementcollector1]




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