|MadSci Network: Physics|
Carbon nanotubes have a number of interesting properties. At: http://www.pa.msu.edu/cmp/csc/ntproperties/ you can find a good summary of nanotube properties. Your question doubtless has to do with the fact that nanotubes appear to have very high tensile strength and high elastic modulus. Their maximum tensile strength is thought to be about 30 GPa, about 10 times higher than any other material. So, at first glance, it might make sense that since the tensile strenght is so high, it might be able to slice through any softer object, like a nickel/iron meteor. The US Government, for example, is looking into using nanotubes for ballistic protection. See: http://www.asc2002.com/summaries/l/LP-05.pdf There are a range of complex issues involved in your question. First, let's say that you have a nanotube wire (or any wire) stretched between two supports, and you drop a ball of clay on the wire. As the clay hits the wire, the weight of the clay distributes itself along the wire. So the first question is whether the wire is strong enough to support the weight of the clay? I suspect that you can use regular physics to calculate the forces on the wire. Nanotubes are very strong, but they are also very tiny, some only 1 nM in diameter. So an individual nanotube can only support a very tiny force. Obviously, if you have a big enough bundle of nanotubes, you can support the weight of the clay. The next question has to do with toughness and impact speed. Let's again say that you impact a nanotube wire with a ball of clay. If the clay is traveling slowly, the force of the clay against the wire will be gradually and uniformly distributed across all of the nanotubes. If the clay is moving pretty fast, the force of the clay will not be distributed uniformly, but will load the nanotubes in front part of the wire first, while the back of the wire is not providing any support. Nanotubes in addition to having high strength are very, very stiff (high elastic modulus). In other words, they don't stretch very much. So, the nanotubes in the front of the wire are going to tend to break before the nanotubes in back have even started to be loaded. Two other considerations before the nanotube wire is going to be able to cut through the meteor. First, erosion of the wire by the meteor. There doesn't seem to be a lot of information about the hardness of nanotubes; maybe they are close to the hardness of diamond. Nevertheless, the meteor is going to be grinding pretty hard against the nanotube wire. Unless the nanotube wire is very hard, the meteor is going to grind away at the wire, weakening it as it attempts to pull through the meteor. Which brings me to the final consideration. If the nanotube wire is going to cut through the meteor, it will generate a lot of heat due to friction. The wire is going to get hot; then the nickel and iron will chemically react with the carbon. We can look to diamond cutting tools to verify this phenomena. If you have a diamond tipped sawblade cutting through a bunch of concrete, it can perform very well. If, however, there is a significant amount of steel reinforcing bar in the concrete, the saw blade will quickly wear away, even though the steel is softer than the concrete. That is why cubic boron nitride is used in place of diamond when cutting stee. So, when cutting an iron-nickel meteor, the carbon nanotube will simply dissolve away. Summarizing, because of potentially low impact resistance and chemical interaction, my money is on the meteor breaking through the nanotube wire. Even so, it is an interesting thing to think about.
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