Re - Can we now build the space elevator?
Robert Clark
arbitrarily long nanotubes. If simply tied together, the longer
nanotube would be weaker but note even if many short segments were tied
together the resulting decrease in strength would still be only the
same fraction as when two segments were tied together. That is, if the
tensional strength decreased to 60% of a single nanotube when two were
tied together, the tensional strength for when 1 million nanotubes were
tied together end-to-end would still be 60% of a single nanotube. Note
then that the tensional strength of nanotubes is so markedly higher
than other materials the strength of these tied together nanotubes
would still be significantly higher than other materials.
This page gives measured strengths of some common knots:
The Most Useful Rope Knots
for the Average Person to Know
http://www.layhands.com/Knots/
Note that some strengths range down to 43% but most lie in the range
of 60% to 70%.
These small diameter nanotubes would have to be tied into knots. So a
means of manipulating them at the nanoscale would be required. Firstly,
nanotubes at centimeter lengths have been formed, as described in the
Science article "Direct Synthesis of Long Single-Walled Carbon Nanotube
Strands" I cited below.
Another research team has also created centimeter long nanotubes:
Extra-long carbon nanotubes set new record
20 September 2004
http://nanotechweb.org/articles/news/3/9/12/1
A longer strand of tiny tough stuff.
http://www.lamonitor.com/articles/2004/09/17/headline_news/news03.txt
Then their lengths is not a problem for forming into knots, just
their small diameters for manipulation purposes. The "Direct Synthesis
of Long Single-Walled Carbon Nanotube Strands" paper notes the 20 cm
long nanotubes were aligned into approx. 10-20 nm diameter ropes. The
authors make a distinction between *strands* of the nanotubes which
were in the 10 micron diameter range and *ropes* in the 10-20 nanometer
diameter range.
The key distinction is that their measurements of the strand's
strengths show only a small fraction of that estimated for nanotubes.
The reason is that these are not formed from nanotubes all the same
length. They are formed from a conglomeration of nanotubes of varying
lengths. Then the forces holding them together are just van der Waals
forces, rather than the carbon-carbon bonds of nanotubes. In such a
case holding a strand at both ends and pulling allows the separate
nanotubes to peel apart. This is described on the page "Pulling
nanotubes makes thread" I cited below.
However, it is the researchers opinion that the *ropes* are formed of
nanotubes formed all the same length. Then presumably their tensile
strength would be the same as the individual nanotubes. Note then that
devices do exist that can manipulate items at the tens of nanometers
scale:
Nanotube Nanotweezers.
Science, Vol. 286, No. 5447, p. 2148-2150, 10 December 1999
http://www.sciencemag.org/cgi/content/full/286/5447/2148
Fabrication and actuation of customized nanotweezers with a 25 nm gap.
Nanotechnology, 12, p. 331-335, 2001
http://www.iop.org/EJ/abstract/0957-4484/12/3/322
Three-dimensional manipulation of carbon nanotubes under a scanning
electron microscope.
Nanotechnology, 10, p. 244-252, 1999
http://www.iop.org/EJ/abstract/0957-4484/10/3/304
An alternative method for linking the nanotubes together would be to
connect them with nanotube rings:
Ring Closure of Carbon Nanotubes.
Science, Vol. 293, No. 5533, p. 1299-1301, 17 August 2001
http://www.sciencemag.org/cgi/content/full/293/5533/1299
These are closed rings formed from one or more nanotubes. They are
about 540 nm across so several of the ropes would have to be fitted
into the rings. One question would be how to tighten the rings around
the nanotubes once they were fitted into the rings. One possibility
might be to use the piezoelectric effect of nanotubes where they can
lengthen when subjected to an electric field. Then you would apply the
field to the rings to widen them, place the ends of the nanotube ropes
inside, then switch off the power to tighten the rings around the
nanotube ropes.
Note that using the rings as a means of binding the ropes together
means you are using frictional effects to get the nanotubes to hold
together. Then is this any better than the van der Waals forces holding
the "strands" together? I believe it can be as long as you make the
rings stricture tight enough. But if it is made too tight, this would
cut into the nanotube ropes reducing their strength. Then the optimal
degree of tightening would have to be found to maintain the greatest
strength.
Interestingly, the method of knotting the nanotubes together or
binding them by rings might also be applied to the strands, that is, to
the case where the nanotubes are of different lengths held together by
van der Waals forces. You would note the shortest length of the
nanotubes composing a strand and tie knots around the strand or bind it
with a rings at short enough intervals to insure that every nanotube is
held tightly with a tie or knot at least once all along the length of
the strand. Note then there have been several reported cases of
nanotube strands or ribbons macroscopically long but much weaker than
individual nanotubes because they are held together by van der Waals
forces. Then this method of binding them at short intervals may provide
a means of recovering close to the full strength of the individual
nanotubes.
Another question that would need to be answered is how binding
together a group of equally long nanotubes effects the strength of the
nanotubes when the binding is only going around the outer nanotubes.
That is, suppose you created a string made from *individual* nanotubes
bound end-to-end and measured the string's strength. Then you composed
a string by using nanotube ropes that all contained the same number of
nanotubes, say 100, and bound these ropes end-to-end. Would the string
composed of the ropes be able to hold 100 times as much as the string
composed of individual nanotubes? This is asking a somewhat different
question than how knotting weakens the nanotubes. It's asking how
strong a composed string will be when a binding can only go around the
outer nanotubes composing the string.
Bob Clark
************************************************************
Newsgroups: sci.astro, sci.physics, sci.space.policy, sci.materials
From: rgregorycl...@yahoo.com (Robert Clark)
Date: 29 Aug 2004 08:01:49 -0700
Local: Sun,Aug 29 2004 11:01 am
Subject: Can we now build the space elevator?
============================================================
From: Robert Clark (rgregorycl...@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
h...@spsystems.net (Henry Spencer) wrote in message
<news:HyzyF...@spsystems.net>...
> ...
> Given that the nanotubes themselves are far thinner than even a one-micron
> ribbon, any material technology that ties them together into bulky
> materials should work just as well for such ribbons, with some adjustment
> in the details of manufacturing. Even such a ribbon *is* a bulky
> material, when the fibers involved are nanotubes.
> ...
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
http://www.sciencemag.org/cgi/content/full/296/5569/884
However, the theory is that this is because there were many single
nanotubes connected together by weaker van der Waals forces rather
than the stronger carbon-carbon molecular bonds that prevail in
individual nanotubes. This is explained here:
Pulling nanotubes makes thread
http://www.trnmag.com/Stories/2002/103002/Pulling_nanotubes_makes_thread_103002.html
What still needs to be tested is the strength of the *individual*
nanotubes that make up these 20 centimeter long strands.
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.
http://www.msnbc.msn.com/id/5792719/
Bob Clark
************************************************************
Ian Stirling
> In the post copied below I discussed tying together nanotubes to get
> arbitrarily long nanotubes. If simply tied together, the longer
> nanotube would be weaker but note even if many short segments were tied
> together the resulting decrease in strength would still be only the
Probably not needed.
I experimented with taking two strands of kevlar string (maybe 100 fibers)
intermingling the fibers over 1/3 of their length (1m) and gluing the
two strands together with silicone adhesive.
The result was almost as strong as the kevlar.
jbuch
KNOTS TO YOU
Yes, there is some data on the strength reduction of macroscopic ropes
being tied into knots.
The question is "Who would assume that the physics of knots scale down
to NANOtubes.......?????"
Not I.
You can't tie a good knot into a single strand of graphite fiber or
glasss fiber.
WHY ? ?
If you calculate the strain of a knot in a single filament (mostly
simple physical geometry is all you need), the strain is typically on
the order of 50% to 100%.
The failure strain of glass fiber might be as high as 10%, and the
failure strain of a graphite fiber will be well under 10%.
So, before the knot is tied, the fiber is broken. The failure strain is
exceeded.
Fishermen know that you can tie knots in reasonably ductile polymeric
monofilament line and the stretchiness of the line is important for the
knot to work.
That is that the monofilament has enough elongation at failure that the
knot does not cause brittle failure upon being tied.
You have a KNOTY problem.
You seem to have great personal tenacity in this technical issue pf |
"Space Elevator".
Keep on trying. But not tying.
Robert Clark wrote:
--
...............................
Keepsake gift for young girls.
Unique and personal one-of-a-kind.
Builds strong minds 12 ways.
Guaranteed satisfaction
- courteous money back
- keep bonus gifts
Robert Clark
> POOR SCALING IDEA ???
>
> KNOTS TO YOU
>
>
> Yes, there is some data on the strength reduction of macroscopic ropes
> being tied into knots.
>
> The question is "Who would assume that the physics of knots scale down
> to NANOtubes.......?????"
>
> Not I.
>
> You can't tie a good knot into a single strand of graphite fiber or
> glasss fiber.
>
> WHY ? ?
>
> If you calculate the strain of a knot in a single filament (mostly
> simple physical geometry is all you need), the strain is typically on
> the order of 50% to 100%.
>
> The failure strain of glass fiber might be as high as 10%, and the
> failure strain of a graphite fiber will be well under 10%.
>
> So, before the knot is tied, the fiber is broken. The failure strain is
> exceeded.
>
Their stiffness may indeed make bending individual tubes them into
knots difficult. However, Fig. 1 in the "Direct Synthesis of Long
Single-Walled Carbon Nanotube Strands" paper shows the much thicker
*strands* (approx. 30 micron diameter) can be bent into knots. However,
this may be due to their being not as stiff or strong due to the van
der Waals bonds between the nanotubes here.
There have been reports though of nanotubes being formed into coils:
Nanocoils spring into place.
http://nanotechweb.org/articles/news/2/8/8/1
From the diameters of the coils I would say these are more likely
ropes of nanotubes rather than individual nanotubes, but this would be
sufficient for our purposes.
Another posibility is to induce the bending in the tubes while they
are being formed. This research shows quite sharp bends can be formed
in this way:
NANOTECH ADVANCE MAKES CARBON NANOTUBES MORE USEFUL.
"San Diego, CA, April 11, 2005 -- Researchers at UCSD have made carbon
nanotubes bent in sharp predetermined angles, a technical advance that
could lead to use of the long, thin cylinders of carbon as tiny
springs, tips for atomic force microscopes, smaller electrical
connectors in integrated circuits, and in many other nanotechnology
applications."
http://www.jacobsschool.ucsd.edu/news_events/releases/release.sfe?id=368
Bob Clark
Ian Stirling
> POOR SCALING IDEA ???
>
> KNOTS TO YOU
>
>
> Yes, there is some data on the strength reduction of macroscopic ropes
> being tied into knots.
>
> The question is "Who would assume that the physics of knots scale down
> to NANOtubes.......?????"
>
> Not I.
>
> You can't tie a good knot into a single strand of graphite fiber or
> glasss fiber.
>
> WHY ? ?
>
> If you calculate the strain of a knot in a single filament (mostly
> simple physical geometry is all you need), the strain is typically on
> the order of 50% to 100%.
However, nanotubes seem to buckle, rather than break.
So, it's likely possible that they could sustain being knotted.
You'd need bloody small knitting needles though, and I doubt that
the strength would be as high.
I suspect that it's pretty irrelevant if you can align long fibers
in a composite rope, if the substrate is at all elastic, even if it
doesn't grip the long fibers well, it should work.
jbuch
The essential point is still true. Scaling Laws.
One canot just grab a macroscopic correlation - like the one on knots -
and project it down to the nano-scale without some honest thinking.
There is often a lack of honest thinking in the "Space Elevator"
cheering section. But, the desire is so high, that it is to be expected
that all straws of hope will be grasped.
Macroscopic ropes are fairly strong even if the fibers are discontinuous
and there is no "glue". But there is a reason for this.
Robert Clark
See the images here:
Carbon nanotubes.
http://www.3rdtech.com/carbon_nanotubes.htm
These bends were induced by a device called the NanoManipulator:
NanoManipulator™ DP-100/200
http://www.3rdtech.com/NanoManipulator.htm
Bob Clark
Robert Clark
> This page shows sharp bends can be made even in individual nanotubes.
> See the images here:
>
> Carbon nanotubes.
> http://www.3rdtech.com/carbon_nanotubes.htm
>
> These bends were induced by a device called the NanoManipulator:
>
> NanoManipulator™ DP-100/200
> http://www.3rdtech.com/NanoManipulator.htm
>
>
> Bob Clark
>
>
This article from doing actual measurements found a highest strength of
63 GPa:
Strength and Breaking Mechanism of Multiwalled Carbon Nanotubes Under
Tensile Load.
SCIENCE, VOL 287, p. 637-640, 28 JANUARY 2000
http://bucky-central.mech.northwestern.edu/RuoffsPDFs/science-9.pdf
However, in some of the cases the attachments broke before the
nanotubes. It is a little unclear if they are including in their
reported cases the nanotubes for which the attachment broke first:
"A deposit at least 100 nm
square was typically made at each MWCNT/
AFM tip interface and was usually a strong
enough attachment to allow the loading and
breaking of MWCNTs before the attachment
failed (20-22). For the MWCNTs in the current
sample set, about half would become
detached at one of the deposit sites during the
tensile-loading experiment. We report here
the results from the successful mounting, tensile
loading, and breaking of 19 MWCNTs."
p. 637.
In any case the force required to break the nanotube itself in the
cases where the attachment broke first would be unknown. Therefore it
is possible some nanotubes have strength higher than 63 GPa.
And this report showed measured tensile strengths up to 150 GPa:
Direct mechanical measurement of the tensile strength and elastic
modulus of multiwalled carbon nanotubes.
B.G. Demczyk et al.
Materials Science and Engineering, A334 (2002), 174, 173-178.
http://cumings.stanford.edu/PDF%20Publications/16.MSE%20A334demczyk.pdf
They also showed examples of inducing sharp bends in individual
nanotubes which suggests the possibility of tying the tubes into knots.
In fact the strength may actually be *better* than that quoted. Both
of these studies were done on multiwalled tubes since they are larger
and it's easier to make attachments with them.
In the earlier study in Science, the authors from SEM imaging noted
that it was actually the outer single-walled nanotube that broke first
therefore it was carrying the load. This would make sense from the way
the attachments were formed which could only form a bond with the outer
surface of the multiwalled tube. Therefore the numbers quoted were for
the strength of this outer single-walled nanotube using as thickness
only that of this single-walled nanotube.
However, in the later study in Materials Science and Engineering, the
authors believed the attachments were made to all the layers of the
multi-layered nanotube. Therefore they took the cross-sectional area to
be the cross-section of the multi-walled tube viewed as a filled-in
*disk*. This is a key fact because it means the strength of this
multiwalled tube is actually higher than the quoted value because it is
actually hollow between the layers. The authors could not calculate the
more accurate cross-sectional area because of the uncertainty in the
number and size of the single layers within the multi-walled tube.
This means the specific strength, the strength to density, will also be
*higher* because the actual density is found by looking at the
individual layers and this will be the same as that of a single-walled
nanotube.
Bob Clark
Robert Clark
ft., 5 km:
TETHERED AEROSTAT RADAR SYSTEM.
http://www2.acc.af.mil/library/factsheets/tars.html
This page explains the tether made of Kevlar has embedded electrical
conductors within it to send power up to the balloon, up to 80 kW, and
metallic braids within it to safely conduct lightning to ground:
What Is a Tether?
http://www.tcomlp.com/aerostats_What_teth.html
This would be a good place to get actual performance data on tethers
kilometers long to see how well their strength to density parameters
hold up at kilometer lengths.
Some reports have studied the feasibility of even longer tethers. This
report recommends tethered balloons for astronomical research at up to
12 km high, 40,000 ft:
POST: A polar stratospheric telescope for the Antarctic.
Publications Astronomical Society of Australia, vol. 13, no. 1, p.
48-59.
http://adsabs.harvard.edu/cgi-bin/b...PASA...13...48D [full text]
And this study recommends tethered balloon astronomy platforms at
65,000 feet, 20 km:
Very high altitude tethered balloon feasibility study.
AIAA Lighter-Than-Air Systems Technology Conference, 11th, Clearwater
Beach, FL, May 15-18, 1995, Technical Papers (A95-30317 07-01),
Washington, DC, American Institute of Aeronautics and Astronautics,
1995, p. 46-51.
http://www.aiaa.org/content.cfm?pag...paper&gID=82068
This article is not available for free, but I gather from the page
freely available online that the authors believe the tether can be made
of Kevlar to reach this altitude.
Bob Clark
Robert Clark
The URL's for those links should be:
POST: A polar stratospheric telescope for the Antarctic.
Publications Astronomical Society of Australia, vol. 13, no. 1, p.
48-59.
http://adsabs.harvard.edu/cgi-bin/bib_query?1996PASA...13...48D [full
text]
Very high altitude tethered balloon feasibility study.
AIAA Lighter-Than-Air Systems Technology Conference, 11th, Clearwater
Beach, FL, May 15-18, 1995, Technical Papers (A95-30317 07-01),
Washington, DC, American Institute of Aeronautics and Astronautics,
1995, p. 46-51.
http://www.aiaa.org/content.cfm?pageid=406&gTable=mtgpaper&gID=82068
Here are some other refs:
Very high altitude tethered balloon parametric sensitivity study.
Surjit S. Badesha, Anthony J. Euler, and Larry D. Schroder (TCOM,
Columbia, MD)
AIAA-1996-579
Aerospace Sciences Meeting and Exhibit, 34th, Reno, NV, Jan. 15-18,
1996
http://www.aiaa.org/content.cfm?pageid=406&gTable=mtgpaper&gID=9032
Very high altitude tethered balloon trajectory simulation.
Surjit S. Badesha, Anthony J. Euler, and Larry D. Schroder (TCOM,
Columbia, MD)
AIAA-1996-3440
AIAA Atmospheric Flight Mechanics Conference, San Diego, CA, July
29-31, 1996, Technical Papers (A96-35084 09-08)
http://www.aiaa.org/content.cfm?pageid=406&gTable=mtgpaper&gID=10354
Dynamic Simulation of High Altitude Tethered Balloon System Subject to
Thunderstorm Windfield.
S. Badesha and J. Bunn, Johns Hopkins University Applied Physics
Laboratory, Laurel, MD
AIAA-2002-4614
AIAA Atmospheric Flight Mechanics Conference and Exhibit, Monterey,
California, Aug. 5-8, 2002
http://www.aiaa.org/content.cfm?pageid=406&gTable=Paper&gID=4227
Bob Clark
Puppet_Sock
[snip]
> The result was almost as strong as the kevlar.
Yes of course. For suitable values of "almost."
Socks
Ian Stirling
>0.9 times as strong, in the test I did.