Photonics

> I agree completely. Just sounded like a neat idea for the
future. It's
> something of the carbon nanotubes category of things that would be
nice to
> have for space development --- nice to have, but not necessary.
>
> Ron
> ******

You mentioned carbon nanotubes. I'm crossposting this message from
the spacesettlers group that was posted by Al Globus today.

TangoMan

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