============================================================ From: Robert Clark ( snipped-for-privacy@yahoo.com) Subject: Re: beanstalks (was Re: Metallic hydrogen ...) Newsgroups: sci.physics, sci.astro, sci.space.policy, sci.materials, sci.energy Date: 2004-06-09 02:06:53 PST
snipped-for-privacy@spsystems.net (Henry Spencer) wrote in message news:...
Tie? Hmmm. Do you think it might work to tie the ends together of the 20 centimeter long nanotubes already produced? Looking up some links on knots, the knotted ropes always have less strength than the single, unbroken ropes. I confirmed this by testing on sewing thread. Still it might be interesting to find out how strong they are compared to single nanotubes.
Bob Clark ============================================================
Testing with thread confirmed that a break always occurred where two strands were tied together. However, to estimate the strength of a single strand of thread, I wrapped two ends around my fingers and found that the break occurred in the middle of the thread, not where I was holding the thread. My guess was that the softness of my fingers prevented the thread from breaking at the attachment point (where I was holding it.) I confirmed this by holding one end by a pair of pliers and the other end with my fingers. The break occurred where the pliers held the thread. However, when I put a soft cloth between the thread and the pliers, the break occurred in the middle of the thread, as when I was holding both ends with my fingers. I imagine this must actually be a common way of testing tensile strength. That is, you don't want to attach the strand or rope to something that will make the rope break at the attachment point. This would give an invalid measure of the rope strength. You want it to break somewhere in the middle. I therefore suggest connecting together the already produced 20 centimeter long nanotubes with a soft material or by whatever means used to insure nanotubes don't break at the attachment point during tensile strength testing. This will allow the full strength of the nanotubes to be maintained even when they are connected together. What will need to be investigated is what soft material will also be light enough so as not to cancel out the weight savings of using the nanotubes. Note that this soft material might be heavier than the nanotube material but because it only has to be used at the connections it can be quite small so quite conceivable may only add minimally to total weight. It still needs to be confirmed that the macroscopic sized nanotubes really are as strong as the nanotubes tested on the microscale. This report showed that 20 centimeter interwoven strands were significantly weaker than the tested individual microscale nanotubes:
Direct Synthesis of Long Single-Walled Carbon Nanotube Strands. Science, Vol 296, Issue 5569, 884-886 , 3 May 2002
Pulling nanotubes makes thread
This article describes a group that proposes that competively offered prizes could make possible the technologies required for the space elevator by 2010:
Space elevator contest proposed. ?Elevator:2010' aimed at encouraging technology development.
Bob Clark