# 3900 byaglobus@... on May 23, 2003, 3:49 p.m.
Member since 2021-10-03
Code IN is the supercomputer/nanotechnology division at NASA Ames
> Code IN Highlights
> May 22, 2003
>
> The Breaking Strength of Carbon Nanotubes Predicted Under Realistic
> Experimental Conditions
> Dr. C. Wei (Eloret/Code ASN), Dr. D. Srivastava (CSC/Code INR), and
> Prof. K. Cho (Stanford University) recently published technical papers
> in Physical Review B, and Applied Physics Letters on the breaking
> strength of carbon nanotubes (CNTs). Identified as ultra-light, very
> strong reinforcing fibers for multifunctional composite materials for
> aerospace structural and shielding applications, accurate measurements
> of the durability of CNTs are vital. Historically, the breaking
> strength has been overestimated due to time-scale limitations of
> computer simulation approaches. Using combined modeling and simulation
> methods to bridge time-scales differing by orders of magnitude, the
> team predicts the breaking strength of defect-free CNTs (at
> experimentally feasible timescale/temperature conditions) is between
> 90-120 GPa (Giga Pascals) versus earlier predictions of 250-300 GPa.
> POC: Deepak Srivastava, Code INR, Ext. 4-3486
> Funded Program: CICT
>
> Background Data:
> Characterization of intrinsic mechanical properties of carbon
> nanotubes (CNTs) is important for their use in synthesis and
> applications of CNT-reinforced polymer or ceramic composite materials
> for lightweight, strong structural, and heat/radiation shielding
> composite materials, respectively.
>
> Discovered about 12 years ago, nanotubes were initially predicted to
> have a breaking strength as high as 25-30% of tensile strain (about
> 300 GPa). Experiments performed in 2000-2002, however found that
> bundles of single- and multi-wall CNTs break at only about 6-12%
> tensile strain (about 60 - 120 GPa) - much smaller than values
> predicted earlier from extensive simulations. The orders of magnitude
> difference between the rate at which nanotubes are strained in
> experiments and what is possible to simulate (due to algorithmic and
> computational power limitations) with current capabilities may be
> responsible for this discrepancy.
>
> Dr. Chenyu Wei and Dr. Deepak Srivastava of NASA Ames and Prof. K. Cho
> of Stanford University have recently proposed and modeled an approach
> that overcomes this limitation of current computational capabilities.
> They predicted the breaking strength of CNTs is 9-12% tensile strain
> (about 90 -120 GPa) - more in-line with experimental observations. The
> key component of success for this "new" combined modeling-simulation
> based approach is to first time reveal a pathway or a bridge to
> connect the computer simulated breaking of nanotube data, obtained at
> pico- to nano-second time scale, with experimental measurements of the
> same taken at minutes to hour time scale.
>
> The technical approach, results, and comparison with experimental
> observations are published in two papers: "Tensile strength of carbon
> nanotubes under realistic temperature and strain rate", C. Wei, K.
> Cho, and D. Srivastava, Phys. Rev. B, Vol. 67, Pg. 115407 (2003, and
> "Tensile yielding of multiwall carbon nanotubes", C. Wei, K. Cho, and
> D. Srivastava, Appl. Phys. Letters, Vol. 82, Pg. 2512 (2003).
> --
>
The materials in one asteroid (the largest ) are sufficient to make
orbital space colonies with ~500 times the surface area of the Earth in
usable real estate. See http://lifesci3.arc.nasa.gov/SpaceSettlement/
for details.
Al Globus
CSC at NASA Ames Research Center
http://www.nas.nasa.gov/~globus/home.html
Views expressed in this email are only my opinions and are not the
position of any organization I'm familiar with.
# 3901 byepibeemie@... on May 23, 2003, 5:08 p.m.
Member since 2021-10-03
OK the non-engineers in this group are dying to know what the implications
of this research are for space elevator development.
# 3902 byian.woollard@... on May 23, 2003, 6:05 p.m.
Member since 2021-10-03
Brad Walsh wrote:
>of this research are for space elevator development.
>
You need about 65 Gpa to build a space elevator without any safety
factor. If the overall strength was 120GPa it would be easily good enough.
90 Gpa might work, but is more marginal.
For comparison, airliners use a safety factor of about 100%. Rockets
often use about 10-20%.
So, I think it doesn't rule it out; this new theory matches experimental
values, the experimental values are about good enough anyway.
> > The Breaking Strength of Carbon Nanotubes Predicted Under Realistic
>
>>>Experimental Conditions
>>>is between 90-120 GPa (Giga Pascals)
>>>
>>>
>
--
-Ian
Motto: "You're Not Authorized to Know Our Motto."
So, like, how many lives DOES Shroedinger's cat have anyway?
# 3903 byaglobus@... on May 23, 2003, 6:14 p.m.
Member since 2021-10-03
Carbon nanotubes aren't as good as we thought. I don't know enough
physics or materials science to know the exact implications for a space
elevator, but it certainly isn't good. Also, this is theory, not
experiment, and the nanotubes are assumed to be defect free. Real
nanotubes will probably be even weaker.
> OK the non-engineers in this group are dying to know what the
> implications
> of this research are for space elevator development.
>
>> The Breaking Strength of Carbon Nanotubes Predicted Under Realistic
>>> Experimental Conditions
>>> is between 90-120 GPa (Giga Pascals)
>
> Questions.
>
The dinosaurs were destroyed by an asteroid because they weren't
space-faring. It's almost as if Gaia then thought "Well, dinosaurs
worked pretty well, but space-faring is necessary. Maybe I'll should
try mammals this time." Humanity is now developing systems to detect
and deflect asteroids, and could build orbital space colonies to spread
beyond Earth to insure life would survive a planetary catastrophe.
Al Globus
CSC at NASA Ames Research Center
http://www.nas.nasa.gov/~globus/home.html
Views expressed in this email are only my opinions and are not the
position of any organization I'm familiar with.