Kevlar vests weigh about 10 pounds and can stop most handgun rounds, but not rifle rounds. What would a vest of nanotubes that can stop handgun rounds weigh, and how thick would it be? How thick & heavy would one that can stop rifle rounds be?
I believe I read somewhere that the traditional method of creating nanotube sheets rivaled kevlar and mylar, but those where very short nanotubes filters and dried much like paper is made.
This new method of creating very long sheets of continuous nanotubes would change all that, I suspect, but afaik, the process is new enough that such tests haven’t been done yet, and the properties under such conditions are still waiting discovery.
We shall have to all wait with baited breath, until we know what companies to invest heavily in.
The nanotube fiber is much strong as it is 60 times stronger than steel but someone has to help me with the vest part. I believe it is not just stopping the bullet but also absorbing the impact that counts. There would still need to be some sort of bulk to absorb the impact.
Do Kevlar vests really weigh about 10 pounds, I thought they weighed more?
Perhaps a link?
[http://www.dupont.com/kevlar/whatiskevlar/whatiskevlar_main.html[/URL
]
[URL=http://www.detnews.com/2005/technology/0508/20/tech-286641.htm]http://www.detnews.com/2005/technology/0508/20/tech-286641.htm](http://www.dupont.com/kevlar/whatiskevlar/whatiskevlar_main.html)
So it looks like it should be better and lighter.
As for the weight of the Kevlar vest I assume it varies depending on if it has inserts and what sort of inserts.
There is a new way yo make long nanotubes? Last I heard (maybe a year ago or so) was the longest nanotube made was only several centimeters long. Doubtless they will improve on that but I was under the impression it would be awhile yet before the stuff could be made very long.
Anyway, not sure how to apply all the following numbers but maybe this will help.
Tensile Strength:
Kevlar: 3.6 GPa (gigapascals)
Single Walled Carbon Nanotube: 63 GPa
So…a helluva lot more tensile strength.
However, if I am reading this right carbon nanotubes are not very elastic. Actually…I have no clue what this page on Young’s Modulus (or Modulus of Elasticity) is telling me. Nanotubes are right next to diamonds on this scale with high strength concrete waaaay down the scale. Aluminum has a higher number than the concrete. If elastic means what I think it means I would think aluminum was more elastic.
Maybe someone can enlighten us.
Don’t know how long this link is good, but their vest are only 3-6 lbs.
This would indicate (to me) that Nanotubes will only make vest stronger not much lighter.
http://www.afmo.com/product_page.asp?pid=3402&referrer=Froogle
I was given about a quart of what was represented as nanotubes.
This stuff wouldn’t be worth a flip for body armour.
Finer than frog hair, blacker than outer darkness, softer than a baby’s backside and slicker than pschit.
Disturb it the least bit and it raises a dark cloud, sticks to skin, everythhing else in sight and is most difficult to scrub away.
You’re reading it right. Materials with a high Modulus of Elasticity are not flexible. They could probably use carbon nanotubes as plate armor, but actually weaving the vest out of nanotubes might not be possible.
You can think of Young’s Modulus as a measure of elastic stiffness. But that is only one half of the story. First you need to know what elastic stiffness actually means!
Materials have a stress range (or deformation range, if you prefer) in which they behave elastically, i.e. bend them and they spring back. However, exceed that range and they don’t behave elastically any more - they either yield, i.e. bend and stay bent, or fracture, i.e. break.
Paper clip wire and a sewing needle of the same diameter have the same elastic stiffness. However, we percieve the paper clip as being much less stiff. In truth it isn’t less stiff, it just yields at a much lower stress. If you bend the paper clip a weeny bit, it will spring back. Bending the needle the same weeny amount takes the same force, so they are equally elastic. But bend them both a bit further and you take the paper clip beyond it’s elastic limit, so it yields or gives, whereas the needle is still elastic and is pushing back against the bending force.
From the Wiki page, aluminium is stiffer than concrete, and bronze and steel are stiffer than glass. This is counter-intuitive, but it is the same as the example I gave above. If you made identical bars of aluminium, steel, glass and bronze, gripped one end in a vice and hung very small weights off the other ends, you will find that concrete and glass deflect further than aluminium and bronze and steel for the same weight. The reason we don’t normally think about the elasticity of concrete and glass is that anything above a tiny deflection and they crack. This isn’t always the case though - thin glass fibres are noticeably elastic, and glass has been used to make springs for sensitive balances.
For making vests, the most important quality of a fibre is energy absorption. You can’t get the total energy absorption from the stiffness or the ultimate strength - what you need is the stress-strain curve - a graph of increasing load and increasing deflection, to the fracture point. The larger the area under than curve, the more the energy absorption. For non-brittle materials, most of the energy absorption occurs due to non-elastic effects and the stiffness is irrelevant.
Back to the OP - the answer is, insufficient data! Until a stress-strain curve is available for the new material, it simply cannot be answered. Carbon fibre is stiffer and stronger than Kevlar, but isn’t so great for energy absorption and doesn’t make good vests. Glass is stiffer and stronger than rubber, but it is rubber sheets used to protect bird boxes from woodpeckers, not glass.
The abstract below indicates an elastic range of at least 5.8% strain for single nanotubes. If the bulk material has similar properties, that suggests an outstanding ability to absorb energy elastically, although the total energy absorption may still not be as good as some other fibres.
On the other hand, you could make a hell of a catapault!
Thanks matt. That clears things up a bit for me.
What I am still lcurious about is how they measure elasticity over time. For instance, we have all probably experienced trying to push a not very sharp (or pointy) object through something like packing tape and the stuff just strecthes and stretches without breaking. We then give it a quick poke and whatever it is we are using pops right through the tape. Or perhaps you have taken a branch and bent till the two ends touch but if you bend it quickly it snaps. I do not see how this is accounted for in the elsaticity measurements.
I ask partly out of curiosity and partly because it seems relevant. Bullets seem to have a puncturing effect based their speed more than that they are sharp or pointy and a material that would seek to stop one would have to manage to overcome that.
There’s additional properties involved. When you load a truly elastic material, it deflects a certain amount and then stays there, more or less forever if the load stays constant. That’s why we can build a steel frame building without worrying about it slumping over time. Within reasonable limits, the elastic behaviour doesn’t change very much with the loading rate.
However, some materials are viscoelastic - apply an instantaneous load and they deflect elastically, but they then slowly extend under the load with time, like molasses. Then there are materials where the properties actually change with the deformation rate, like silly putty and non-drip paint. You can’t model these materials with simple elastic-plastic assumptions.
You are quite correct in that the rapid deformation involved in stopping a bullet may cause the material to behave differently to predictions made from slow strain-rate experiments. Or it may not! You have to do additional experiments to determine whether there is a rate effect.
That would be bated breath.