Sciencemadness Discussion Board - [Metalurgy] Homemade steel body armor

[Metalurgy] Homemade steel body armor

joseph6355 - 2-1-2018 at 19:40

Is anyone interested in the idea of making their own steel body armor?

First of all, lets pay attention to some principles when making hard body armor.

A lot of people talk about ar500 and ar600, but those are industrial nomenclatures, and not actually steel chemical standards. It means that ar500 isn't actually a steel alloy, but just a market-friendly way of describing a certain type of steel that has been exposed to certain heat treatments.
AR stands for abrasive resistant. It means that there are chemical additives (alloys) that are mixed within the molten steel in order to achieve resistance to abrasion (it will suffer less from wearing when scratched with a harder element). Generally, Manganese, Phosphorus, Chromium and Boron are added in certain quantities to obtain such characteristics.
500, 600 and so on, stands for the Brinell hardness of the metal. 400 is not enough if you want it to last, 500 is ok, 550 is good, 600 is ideal if you chose the proper thickness for the armor plate. Don't go above 600 or else it will get so brittle that it will shatter (specially after a few shots from a heavy hitter). Choosing the proper steel alloy is the key. The most important factor to stop a projectile is the final hardness, but the added alloys also imply in a greater bullet-stopping capability, specially Manganese and Phosphorus in higher quantities, and also add toughness to the hardened steel so it is hard but not as brittle as other less tough steel alloy would be at the same hardness.

Steel alloys
The most easy-to-get steel alloy that will suit these needs is the AISI 5160. It is frequently used in leaf springs, so it became readily available and cheap. At 600 Brinell, you can get away with .210 gauge thickness, but back face deformation will also be greater, and thus, increase the chances of an injury. The pro side is that it will be slightly lighter.
I would personally go for the 1/4" thick plate, it will be more robust and last longer, and also compensate for any human error that could be made that would reduce its bullet-stopping capabilities. Another key factor is grain refining. Normalizing the steel will reduce the grain size and increase the plate toughness, because the kinetic energy delivered by the projectile will be more evenly distributed among the greater number of grains. Think about it as hitting a bucket filled with fine sand with a hammer, and then hitting another bucket filled with gravel. Which one do you think that will result in a higher penetration depth?

Heat treatment
In order to heat treat it correctly, you could send it to a heat treating company. But it would totally defeat the "homemade" purpose of the thing, right? You could build a gas forge, and judge color by the eye.
Not a very accurate reading, but if its the best you can do...
AISI 5160 is very forgiving when heat treating though.
You will need to heat it to a red-orangeish color and then let it cool to black, and wait a few minutes then. Do it 3 times.
Next, heat it again to the same color and quench it in a fast coolant, like olive oil or parks 50 oil. Agitate it gently.
Next, put it in the oven and use an accurate temperature reading, like a good thermometer. Temper it to 200-210 ºC for 1 hour, and then let it cool to room temperature.

And remember to curve or form the plate before you heat treat.
A lot of companies complain that 600 Brinell steel cant be bent and curved, so they don't use it.
Well, they shouldn't be bending the hardened steel in the first place, it will cause a lot of stress in the material and compromise toughness.
All forging, curving and cutting should be performed prior to normalizing and hardening.
The true reason why they do this is because they buy the steel from a proprietary company that don't disclose the alloy used neither how to heat treat it, and then they don't have other option but to curve the hardened steel.
Common abrasive resistant borderline-proprietary alloys used in body armor are T1, T2, T3 and so on. AISI 5160 gets very close to some of these abrasive resistant alloys, and it is both tough and capable to achieve high hardness.

Thickness
First of all, lets talk about what the NIJ standards call for.

https://www.ncjrs.gov/pdffiles1/nij/223054.pdf
Type III hard armor or plate inserts shall be tested in a conditioned state with 7.62 mm FMJ, steel jacketed bullets (U .S. Military designation M80) with a specified mass of 9.6 g (147 gr) and a velocity of 847 m/s ± 9.1 m/s (2780 ft/s ± 30 ft/s).
That is what a level 3 body armor should be able to stop.
Commercial body armor are mostly 1/4" thick and have a hardness of 500 to 550 Brinell. At this hardness and thickness, it will stop most projectiles traveling under 2900 ft/s (for 5.56) and 2800 ft/s (for 308 win).
Newer plates though have an increased hardness at about 600 Brinell, and some going even further till 650 Brinell.
Spartan armor plates have a thickness of .210 inches, and 600 Brinell hardness, and will stop 5.56 projectiles traveling under 3200 ft/s. That is a huge improvement, since a 55 grain projectile traveling that fast would penetrate a common ar500 plate.
The problem with a hardness like this is that the plate will be prone to shattering. To counteract that, we can try to refine the grain and increase the thickness. A thicker plate will accept an increased hardness better.
It is also proven that ar500 1/2" thick plates will stop a .50 BMG FMJ traveling under 3200 ft/s. But if you are going to get hit with a .50 BMG, the kinetic energy itself would probably kill you anyway, because there isn't enough surface are to distribute this energy that would allow it to be reduced to an acceptable level. So just take your armor off and die like a man.

Anti-spalling coatings
You can always pay someone to coat your plate with bedliner. There are places that will offer this kind of service. But I'm gonna focus on the fun part, which is making it yourself.
You could coat it with bedliner yourself, but it is kind of expensive, messy and complex. So we will use fiberglass.
You see, fiberglass and epoxy are perfect for this. The final product will be a hard plate that will not only help with slowing down the projectile, but contain its spalling.
The projectile will penetrate the fiberglass plate and hit the steel, which will make it basically pulverize, but the surrounding fiberglass will catch all of the fragments.
The fragments usually fly at a 20º angle from the plate, so I eyeball a 1/2" thick fiberglass plate to be enough to catch all the fragments.

I think I covered the basics and now we can start a discussion about it. Maybe testing too.
I can't test it with rifles because I live in a country where it's not possible to own it legally, but I'm sure that there are a lot of Americans here that can test it properly.
I've shot a small 10x10 cm plate before with a .38 SPL and .40 SW. No dents, no bending, no back face deformation, no nothing. It wasn't even fun.

[Edited on 3-1-2018 by joseph6355]

elementcollector1 - 3-1-2018 at 09:32

Honestly, if I were going to build a set of body armor, I'd make it from UHMWPE. Far lighter, and just as strong.

unionised - 3-1-2018 at 09:45

Is it just me who thinks this makes roughly as much sense a a DIY parachute?

walruslover69 - 3-1-2018 at 09:53

how are you creating your steel alloy plate in the first place? if you are already buying a steal plate, why not just buy a bullet proof plate?

joseph6355 - 3-1-2018 at 10:41

Quote: Originally posted by elementcollector1

Honestly, if I were going to build a set of body armor, I'd make it from UHMWPE. Far lighter, and just as strong.

I don't know. I hasn't been tested.
Are you sure it will sustain multiple hits from a 5.56 projectile traveling at 3200 ft/s?

joseph6355 - 3-1-2018 at 10:46

Quote: Originally posted by walruslover69

how are you creating your steel alloy plate in the first place? if you are already buying a steal plate, why not just buy a bullet proof plate?

For the sake of experimenting and creating something with my own hands.
What if some day you are not allowed to buy armor plate anymore? What if the government requires it to have a serial number? What if...
Nothing wrong with testing and having the knowledge.

I don't want to depend on the government or any private company to protect myself from rifle threats.

"why not just buy a bullet proof plate?"
Why buy it in the first place if I can make my own?
It will be far cheaper and have the same efficiency.

joseph6355 - 3-1-2018 at 10:58

Quote: Originally posted by unionised

Is it just me who thinks this makes roughly as much sense a a DIY parachute?

Yeah, lets just rely on the government and private companies to protect ourselves.

Nothing wrong with going online and buying a steel plate. But remember that not so long ago it was possible to buy nitric acid otc, nowadays it became more expensive and hard to get, forcing people to make their own.

MrHomeScientist - 3-1-2018 at 11:42

Quote: Originally posted by joseph6355

It will be far cheaper and have the same efficiency.

...Somehow I doubt that.

I'm not sure what you're trying to do here. Are you trying to make medieval plate armor that's bulletproof?

If you do and you can demonstrate it works just as well as commercial products, definitely post it here. It would be quite the achievement.

Fulmen - 3-1-2018 at 12:48

Quote: Originally posted by joseph6355

You will need to heat it to a red-orangeish color and then let it cool to black, and wait a few minutes then. Do it 3 times.

What would be the purpose of this? Normally one only needs to heat to uniform heat plus 15-30minutes soak time.

Quote:

Temper it to 200-210 ºC for 1 hour, and then let it cool to room temperature.

This will most likely produce a brittle product. While I haven't worked with 5xxx steel I do know a little bit about 4xxx, and it is seldom annealed below 400°C.

walruslover69 - 3-1-2018 at 12:59

you could just stock up and buy plates. they are less than $100. You wont be able to make anything like that for $100. You never answered, how do you plan on making the steel alloy plates in the first place?

unionised - 3-1-2018 at 13:34

Quote: Originally posted by joseph6355

[
Yeah, lets just rely on the government and private companies to protect ourselves.

I guess you make your own bullets, make your own powder + make your own guns too.

Twospoons - 3-1-2018 at 13:52

@joseph6355 Don't listen to the nay-sayers. Have a go.

Its right there are the top of the page: "The Art and Science of Amateur Experimentalism". I'd have thought everyone would be more supportive.

I build or make a lot of stuff I could just go out and buy - but where's the fun in that? What would I learn?

[Edited on 3-1-2018 by Twospoons]

OldNubbins - 3-1-2018 at 15:34

Support should not be conflated with encouragement. What I am seeing are people supporting the OP in a way that ultimately leads away from a misguided effort to solve a problem that does not exist using methods that are likely to be flawed and inefficient, perhaps even ultimately dangerous.

I appreciate the ‘do-it-yourself’ mentality, not for a conspiratorial distrust of large organizations but for a sense of self-improvement and satisfaction. However, in the context of this thread, how much chemistry and how much ‘make-it-yourself’ is actually involved? In my opinion, not much.

In order to experiment and learn, you would need detailed knowledge of the chemical composition of the steel being used. This requires it to be purchased from an organization that can provide material test reports that are generated in accordance with large, untrustworthy organizations such as NIST, ANSI, ISO, etc. That aspect removes the majority of the DIY.

Where will you get your 5160 steel from? Can you guarantee the beat up old Chevy that spring steel was removed from is indeed 5160?

How will you control the heat treating process on something you are entrusting your life to? I used to work at a shop that made gear components for limited-slip differentials. The gears required a combination of through-hardening for overall toughness with a case hardness at a critical depth (too deep and the whole tooth was brittle, too shallow and it would deform). The heat treating process is difficult to control, and really more of an art form with myriad variables. Our vendor was really quite good and yet we would still see over 50% failure rate. Torching your steel to whatever-ish color, saturated with garage atmosphere and quenched in used motor oil with a pad of butter will give me a whatinistic crystal structure of the correct grain size? Will the leaf springs off my Aston-Martin be austen-martensitic enough?

This topic may be better suited to a gun enthusiast or blacksmithing forum. However, if there are some methods for creating some interesting alloys using thermite that don’t result in a large portion of the product violently erupting from an old paint can an a few slaggy chunks of iron, I am all ears.

XeonTheMGPony - 3-1-2018 at 16:57

Quote: Originally posted by unionised

Quote: Originally posted by joseph6355

[
Yeah, lets just rely on the government and private companies to protect ourselves.

I guess you make your own bullets, make your own powder + make your own guns too.

I have, it really isn't that hard you know.

joseph6355 - 4-1-2018 at 06:11

OP here.
I see that you guys are not willing to even consider the idea.
I'll try it somewhere else.

I will not answer anymore questions, I don't think it's worth it since people here seem to be very close-minded.

SWIM - 4-1-2018 at 09:55

You weren't really answering questions in the first place.

Fulmen tried to discuss the metallurgy with you and ask about your annealing procedure but you wouldn't deign to answer.

Walruslover69 actually went full walrus and asked repeatedly for information you wouldn't supply about plate sources.

Your few answers were primarily aimed at justifying your survivalist aims, not explaining the project.

Hard to see what you were expecting.

Unquestioning and universal approval?

Besides, your post reads like you culled your information about armor from PMJB, or the Poor Man's Armorer, or other sources like that as opposed to actually going to the effort to find legitimate, reliable information.

[Edited on 4-1-2018 by SWIM]

Fulmen - 4-1-2018 at 10:07

He's a quitter, good riddance.

donalderrand8 - 24-1-2018 at 03:37

Quote: Originally posted by XeonTheMGPony

Quote: Originally posted by unionised

Quote: Originally posted by joseph6355

[
Yeah, lets just rely on the government and private companies to protect ourselves.

I guess you make your own bullets, make your own powder + make your own guns too.

I have, it really isn't that hard you know.

Tell me it was just for experiement! right?

AJKOER - 31-1-2018 at 08:47

Please explain how something simple and inexpensive as taking many small bags and filling it with peddles (technical speak for small rocks), and inserting it into a wired or otherwise constructed body frame, would not deflect or possibly stop most high speed projectiles? I would envision the need for similar taylormade arm, neck and head protection.

Yes, granted, after testing with real bullets, you may need, worst case, a few new bags and more peddles, but that is to be expected. The fragmentation of the rocks may also injury the person, or persons, shooting at you from close range, and any cloud of particles could obscure your shooter's view along with surprising the hell out of them while the shooter tries to understand what the f**k just happened, but these are likely all positives, not offered by other conventional body armor geared to possibly(?) stopping (and not deflecting) projectiles!

[Edited on 31-1-2018 by AJKOER]

Sulaiman - 31-1-2018 at 09:15

Technically;
peddles = sells
pebbles = small rounded rocks

JJay - 31-1-2018 at 10:11

I bet Damascus steel makes great plate armor.

Fulmen - 31-1-2018 at 14:31

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.

clearly_not_atara - 31-1-2018 at 14:58

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.

Anyway IIRC boron carbide is preferred for this application is it not? At least you don't have to worry about the "grade" as much with B4C. According to this:

https://www.researchgate.net/profile/Robert_Ritchie/publicat...

the most damage-tolerant material is a palladium-based metallic glass with composition Pd79Ag3.5P6Si9.5Ge2. 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 ."

So maybe you can take your seashells down to the seashore and storm the beaches of Normandy, or something.

JJay - 31-1-2018 at 23:03

Quote: Originally posted by Fulmen

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.

Wootz steel is not really damascus. Damascus steel has very thin layers of different steel alloys laminated together, so it resists cracking and shattering the same way that bulletproof glass does.

Damascus steel certainly does rival modern steel, especially if it the steels chosen for the laminate are modern alloys. Some people pay thousands of dollars for a single Damascus chef's knife.

Fulmen - 1-2-2018 at 02:10

The prices modern pattern Damascus can fetch is mainly due to the look and the incredible craftmanship involved. As most patterns will end up crossing the edge both alloys need to have similar mechanical properties to retain a useful cutting edge.
Laminated blades have been made for a long time (Japanese swords for instance), these did combine soft and hard steel for several reasons. One was cost, a good edge-holding carbon steel has historically been expensive. But shatter resistance was also important, the old carbon steels were quite brittle compared to modern steels.

The historical Damascus blades were not forged from different alloys, they did have dark lines/bands but afaik these were formed by precipitated carbides.

I guess part of the disagreement is around the term Damascus. In a more broad sense you could be right, a metal composite could have interesting properties. But at the same time there are probably simpler ways to achieve such properties. One would be case hardening, this produces a hard outer skin while keeping the core ductile.

AJKOER - 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

?

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]

JJay - 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.

joseph6355 - 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.

[Edited on 2/2/18 by joseph6355]

Fulmen - 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.

joseph6355 - 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.

[Edited on 2/2/18 by joseph6355]

Fulmen - 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.

joseph6355 - 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.

AJKOER - 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]

elementcollector1 - 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.

AJKOER - 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]

Fulmen - 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.

AJKOER - 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'.

joseph6355 - 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.

joseph6355 - 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]

elementcollector1 - 3-2-2018 at 22:45

Quote: Originally posted by joseph6355

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]