Repelling bullets with nanotube armors
Australian engineers have found a way to use the elasticity of carbon nanotubes to not only stop bullets penetrating material but actually rebound their force. Their anti-ballistic carbon nanotubes are very different from the current materials used to design bullet-proof jackets, such as Kevlar, Twaron or Dyneema fibers. Current jackets can stop bullets, but the users can still be severely wounded by the strength of the impacts. On the contrary, these future nanotechnology-based jackets not only stop the bullets, but they repel them, thus avoiding 'blunt force trauma.' The research team doesn't say when such bullet-proof jackets might become available.
The figure shown above shows how such a structure works. "The molecular dynamics model of a carbon nanotube subjected to ballistic impact. (a) Initial model, (b) a deformed nanotube at its maximum energy absorption. (Credit: University of Sydney) This research project has been conducted at the Centre for Advanced Materials Technology at the The University of Sydney by Professor Liangchi Zhang with the help of Doctor Kausala Mylvaganam.
So why did these researchers start to work on this project? "Most anti-ballistic materials, like bullet-proof jackets and explosion-proof blankets, are currently made of multiple layers of Kevlar, Twaron or Dyneema fibres which stop bullets from penetrating by spreading the bullet’s force. Targets can still be left suffering blunt force trauma -- perhaps severe bruising or, worse, damage to critical organs. The elasticity of carbon nanotubes means that blunt force trauma may be avoided and that’s why the engineers in Sydney have undertaken experiments to find the optimum point of elasticity for the most effective bullet-bouncing gear."
In "Scientists develop material that bounces bullets," The Telegraph provides some additional details. "The team tested carbon nanotubes down to 0.7 nanometres (billionth of a metres) across, and a length of about 7.5 nanometres, by bombarding them with diamond bullets travelling at speeds varying between 1000 and 3500 metres per second, revealing the conditions when the bullet could bounce back, as the nanotube released energy stored during the initial impact. Based on their findings, they calculate that six layers of woven nanotube yarn - about 600 millionths of a metre thick - may protect the wearer from a revolver bullet, so that it bounces off.
For more information, this research work has been published in the Institute of Physics's Nanotechnology journal under the title "Ballistic resistance capacity of carbon nanotubes" (Volume 18, Issue 47, November 28, 2007, Article 475701). Here is a link to the abstract. "Carbon nanotubes have high strength, light weight and excellent energy absorption capacity and therefore have great potential applications in making antiballistic materials. By examining the ballistic impact and bouncing-back processes on carbon nanotubes, this investigation shows that nanotubes with large radii withstand higher bullet speeds and the ballistic resistance is the highest when the bullet hits the centre of the CNT; the ballistic resistance of CNTs will remain the same on subsequent bullet strikes if the impact is after a small time interval."
After free registration, you will have access to the full technical paper (PDF format, 4 pages, 621 KB). The above figure has been extracted from this document.
Sources: Institute of Physics news release, October 31, 2007; and various websites
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