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Assuming we could get a single nanotube a metre long, would it be possible to break it by hand or would it slice through just about everything including flesh and bone? Could we even grip it, or would we need an anchor at each end?

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    $\begingroup$ Single-walled? Double-walled? What kind of break are well talking about (e.g., compression, buckling, etc)? There's a few details missing, but it is an interesting question. $\endgroup$ – Kyle Kanos Mar 28 '15 at 0:54
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    $\begingroup$ It takes on the order of micro-Newtons to break a nanotube. So even if I tied you up with one, you'd walk free completely unaware of it. $\endgroup$ – lemon Mar 28 '15 at 0:56
  • $\begingroup$ Maybe as I walked away the tube would slice me in half? How strong are skin and muscle cells compared to a nanotube? $\endgroup$ – user56903 Mar 28 '15 at 1:08
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Here's a quick and dirty approximation based on some values reported in Wikipedia:

  • Wikipedia lists the ultimate tensile strength of a carbon nanotube as 63,000 MPa, but in a footnote proposes a "theoretical limit of 300 GPa" for multi-walled nanotubes.
  • Wikipedia also mentions "most single-walled nanotubes (SWNTs) have a diameter of close to 1 nanometer."

Generously assuming the 300 GPa tensile strength limit, a cable of nanotubes 2,000 nanometers wide (containing on the order of a few million individual nanotubes) would most likely snap under the weight of an apple (on Earth):

  • (300 GPa ) * pi * (1000 nm)^2 = 0.9425 N

For comparison, a human hair is roughly 100,000 nanometers wide.

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    $\begingroup$ True. But now work out what the weight of an apple applied to the surface area of that nanotube in your hand would do to you. $\endgroup$ – user56903 Mar 28 '15 at 1:09
  • $\begingroup$ Mmmm but with that theoretical upper limit, the force required to break a cable the size of a human hair would be much greater than that of a human hair...of course that lower limit would make it much less $\endgroup$ – Triatticus Mar 28 '15 at 1:59
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Let's assume a nanotube bundle with a breaking strain of about 1N and a circumference of 5 microns ie 5 x 10^-6m.

It is wrapped around a finger and in contact with the skin for around 0.02m. The area is pressure exerted over that surface is 10 million Newtons per square metre, which is 10 MPa or some 100 times atmospheric pressure.

I think nobody could break it with their hands because it would slice off all their fingers. Unless anyone cares to comment on the resistance of skin and bone to such pressures?

For reference the nanotube is comparable in radius to the edge of a very sharp razor blade. The difference is, the nanotube is "pure edge" with none of the wedge shape characteristics of a knife. When a knife cuts, a lot of the force needed is due to the fact the wedge shape has to push the side of the cut open as the blade goes deeper.

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  • $\begingroup$ The problem with this analysis is that by assuming a value for breaking force as 1N, you do not appear to consider the material properties of the nanotube, such as tensile strength or yield stress, instead turning this into a purely geometrical analysis. Unless the 1N value has some significance with nanotubes? $\endgroup$ – Involutius Mar 29 '15 at 1:28
  • $\begingroup$ True, it is a simplified argument, but as nobody else was giving me a reasonable analysis of the problem I decided to gave a go. BTW, the question is NOT "Does a Human have enough strength to break a carbon nanotube". It is whether trying would slice your fingers off. Over to you... $\endgroup$ – user56903 Mar 29 '15 at 9:30

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