Page 194 - Carbon Nanotube Fibres and Yarns

184 Carbon Nanotube Fibers and Yarns

a
b
the world, such as Q-Flo Ltd., Nanocomp Technologies, Inc., Suzhou
c
d
Creative Nano Carbon Co. Ltd., Super C, Inc., and DexMat. e
Despite the many achievements in the past two periods, there is still
a lack of fundamental understanding on the underlying mechanics of the
CNT yarn structures formed by different spinning methods. As an assembly
material, the mechanical properties of CNT yarns are determined mainly
by the rich intertube forces, rather than by the intrinsic strength of the
individual CNTs. Depending on the yarn formation methods employed,
the yarn properties are affected by many structural parameters, including
the twist level of the yarn assembly, the packing density, alignment, entan-
glement and straightness of nanotubes in the yarn, and the diameter, length,
wall thickness, and surface modification of the constituent nanotubes. Up
till now, these parameters were investigated mainly by controlled experi-
ments. Theoretical modeling is an important tool to discover the underlying
principles behind these parameters and to optimize the yarn structure and
performances. In this chapter, we review recent progresses on the mechanics
modeling and numerical simulation of CNT yarn properties.
We first introduce a widely used yarn geometric model. This is fol-
lowed by models of intertube interactions, especially the sliding friction
that strongly affects load transfer between the CNTs, and then the micro-
structural evolution using molecular mechanics (MM), molecular dynamics
(MD), coarse-grained molecular dynamics (CGMD), and multiscale mod-
eling. In the final part of this chapter, we discuss future research directions
and experiments designed to improve CNT yarn mechanical performance.

8.2 Analytic models for CNT yarns

The term CNT yarn was given due to its structural similarity to traditional
spun yarns made usually by twisting together short fibers (staple fibers).
However, there are also distinct differences between a CNT yarn and a staple
fiber spun yarn. The number of fibers in the cross section of a staple yarn is
usually from about 40 to a few hundred while the number of CNTs in the
6
cross section of a 10-μm-diameter CNT yarn could be up to 1 million (10 )
[36]. Due to the very small CNT diameter, the tube-tube interface or contact

a Established in Nottingham, UK in 2004.
b Established in Lebanon, USA in 2004 and moved to Merrimack, USA in 2012.
c Established in Suzhou, China in 2011.
d Established in Shenzhen, China in 2016.
e Established in Houston, USA in 2015.