Can carbon fiber make a better bulletproof vest?

[Jake]

Hey all,

I wonder if anyone can answer this for me:

Why hasn't carbon fiber been used to make better bulletproof vests (ignoring cost)? Doesn't carbon fiber have a higher tensile strength than Kevlar? Isn't it lighter?

Also, wouldn't a solid version, of carbon fiber reinforced plastic, as thick as an infantry armor plate, also provide great protection?

And how about Carbon Fiber Reinforced Ceramic? Wouldn't that be the ultimate protection? Is there anyway to do this?

These questions have been nagging me for a while, and I can't find anything on the internet. I don't really need this for school or anything, but I figured I'd bring it up anyway :)

Thanks :)

 

[turbo]

Kevlar is used because it is strong and cheap, and can be woven into flexible cloths that can be laminated. A bulletproof vest is not some monolithic material. It is made of materials that can be stacked in thin light layers, that can slow a bullet while spreading its shock over wider and wider areas (which is where the layers come in). There are other very strong fiber materials that can be used, but so far carbon's brittle nature has made it unsuitable for armor. Carbon nano-tubes might one day be woven into suitable strong light fabrics, but it is horrendously expensive now, and would probably require a lot of designing, engineering, and testing to make a safe vest.

Kevlar, while not dirt-cheap is a very strong Aramid fiber that can be mass produced easily, and it is commonly available in consumer products, like the yellow cut-resistant woven gloves you can get at industrial-supply places and food-industry supply places.

 

[Jake]

Hey Turbo,

So it is the brittelness specificly that prevents carbon fiber from being used in vests as a replacement for Kevlar?

I can't visualize this though; carbon fibers still can flex a great deal, much more than a vest actually moves when hit by a bullet. And the whole point of Kevlar is its high tensile strength, which carbon is higher in, so I still don't see what the obstacle is.

 

[turbo]

Kevlar is VERY tough and flexible, and the fibers can be twisted to increase the density and integrity of the woven cloth. This is a major advantage in application. It's important to keep the weave dense enough to reduce projectile penetration, and the more layers can remain intact, the more they will help redistribute (spread out) the force of the impact, reducing blunt-force trauma. A cop might get shot with a pretty high-powered round, and still have heavy contusions, broken ribs, etc, even though the bullet didn't penetrate through the vest.

 

[junewolf]

I realize all of your points but theoreticaly, how many layers do you think it would take to create a vest (kevlar takes 15 layers)

 

[turbo]

I have no idea how many layers might be required in practice. Ballistic textiles have properties that vary with fiber-size, type of weave, etc. Nanocomp has made progress in the "bulletproof" area. Their lightweight carbon nanotube "paper" requires ~100 layers to stop a 9mm round. Remember that even if a bullet cannot penetrate a fiber vest, the deformation on impact may be enough to cause severe internal injuries.

 

[junewolf]

How about just impact resistant? Not nessecarily strong enough to stop a bullet but enough to not break after being hit with blunt force.

 

[NanjoeBot]

I think Carbon may be too brittle. A friend of mine had a Carbon Fiber bike that a car backed into and knocked over. (not going fast) Big shards broke off of it and the body started cracking after that.

 

[lifesaboar]

how easy is it to work with Kevlar? I'm a hog trapper/catcher and use dogs that wear kevlar vest to protect from the wild hogs tusk. Was interested in sewing my own vest rather than pay the marked up prices for retail. Any thoughts or suggestions would be helpful.

 

[pantaz]

how easy is it to work with Kevlar? I'm a hog trapper/catcher and use dogs that wear kevlar vest to protect from the wild hogs tusk. Was interested in sewing my own vest rather than pay the marked up prices for retail. Any thoughts or suggestions would be helpful.

Compared to other fabrics, the only real difficulty is cutting it. Google "http://www.google.com/search?q=shears+for+kevlar"" for plenty of info.

As I understand it, protective vests use layers that vary in weave direction, thread count, etc., to improve penetration resistance. Might be difficult to replicate the commercial vest's performance.

 

[dlgoff]

Compared to other fabrics, the only real difficulty is cutting it.

Yep. I have worn out many scissors blades on the stuff.

 

[JaredJames]

Carbon Nano-Tube Body Armour from Cambridge University:

http://news.bbc.co.uk/1/hi/sci/tech/7038686.stm

Just thought I'd drop this in for the OP.

 

[Jackpot513]

I just found this thread after randomly thinking about body armor and doing a little research, I'm a long time firearms enthusiast and stopping bullets is just as important as putting them where you aim, anyway my ideal is casing the carbon fiber or composite strand with some of the new organic ceramics like hydroxyapatite. It is used to regrow lost bone mass, doesn't require the heat traditional ceramics require as well as opening the possibility of a self healing (organic) lightweight body armor.

 

[AlephZero]

Kevlar can absorb a lot of energy when the fibers stretching plastically and don't return to their original length afterwards.

With carbon fiber, the strain energy only goes into elastic deformation, which is small compared with the plastic deformation of kevlar, but the energy is released again as the fibers goes back their original shape. If the energy (i.e. the internal stress) is too high, carbon fiber would just shatter as the bullet punched a hole through it.

As a "real life" comparison of the difference, on some large jet engines a layer of kevlar (about 2 inches thick) is used to contain the debris if one of the large metal fan blades at the front of the engine breaks off. To give some idea of what that means, the energy in the broken blade is about the same as a compact car plus 4 passengers traveling at 80mph, and the kelvar catches it and stops it dead within the space of about 6 inches.

When GE designed their carbon fiber fan blades for the GE90 (on the Boeing 777) they claimed that it was unnecessary to have a containment system at all, because the carbon fiber blade would just shatter into powder as it hit the metal fan case. The two materials behave very differently given about the same amount of energy to absorb. (The FAA didn't entirely agree with GE's assertion about what would happen to the carbon fiber, but that's not the point of the story).

 

[AR15alltheway]

due to the fact that carbon fiber is brittle would it be a good replacement for ceramics in Small Arms Protective Inserts (SAPI) plates? in a sapi plate the ceramic helps slow down and break up the high velocity projectile while the kevlar,TT34 twaron or Dynemma "catches" the bullet at the reduced speed. yes both the ceramic and carbon fiber break on impact but the point is to provide enough resistance for the actual armor component. my question is will the CF provide enough resistance? and what are the weight savings?

 

[Dummienoob]

A guy recently invented Kryon - a material made up of CNTs and aluminium. The article said that it resisted multiple 50. cal rounds. That would be a pretty good armour but you would still get hurt by the impact.

 

[OCR]

Just thought I'd drop this in for the OP.

A couple more...

http://www.bodyarmornews.com/body-armor-news/liquid-body-armor.htm

http://en.wikipedia.org/wiki/D3o



OCR

 

[F. P. Caro]

graphite kevlar body armor with alumatatium

 

[inquisitivegeek]

AlephZero's answer is the correct one.

Carbon fiber has a high strength but lousy toughness, because it has practically no elongation after its ultimate tensile strength has been reached.

Also because carbon fiber is so brittle, it must be encased in a rigid matrix material like epoxy resin. Which will make the bullet-resistant vest inflexible and impermeable.

Carbon fiber-based composites are in fact so brittle and damage intolerant, that maintenance crews of vehicles constructed from the material must be careful not to knock the composites - a dropped spanner is a common example. Doing so would cause usually invisible damage to the composite and a degradation of up to 70% of its mechanical properties.

Furthermore, carbon fiber based composites do not have a progressive failure mechanism. Most ductile metals do, i.e. they yield, work harden, yield some more, have visible cracks/dents, etc. and then break. A carbon fiber composite that is under heavy loads, and gets damaged, will go bang and break.

Carbon nanotubes and macroscopic carbon fibers are different things, for now. Yes carbon nanotubes show promise as an armor material but they are more expensive per gram than gold.

 

[Brandon Goodrich]

So now there are carbon fiber/Kevlar composites. Has there been any research into the ballistic and impact resistance of these? Rip resistance would also be a good point to measure when considering active use of jackets, pants, etc.

 

[MackMcCoy]

I am working with a patented flexible carbon fiber called CF-Lex .. I believe CF is 5 stronger than steel, is that correct? The flexible carbon fiber maintains 80% of strength. I wonder if we could design a flex matrix.. A combination of hard and CF-Lex. Or just have 100% cf-lex. Any ideas?

 

[JosephJordan12231122]

I have a question what if you layered Kevlar with carbon fibers in making a bullet proof vest put the first layers all kevlar on the outside the start alternating kevlar carbon would that not possibility make the carbon fibers more resistant to weakness while increasing strength?