Biomedical Engineering Reference
In-Depth Information
CNTs possess remarkable mechanical properties because they
are essentially rolled-up graphene sheets. Graphite is very strong
with respect to the in-plane deformations and can support very large
tension. CNTs have tensile strength that is unmatched by any other
known materials [68]. They are not only strong but also extremely
elastic. In fact, CNTs can reversibly bend to very large angles [69].
Salvetat
. [68] measured the elastic and shear moduli of SWCNTs
ropes using atomic force microscopy (AFM). They used a suspended
beam configuration to perform their measurements. Using the AFM
tip to apply a load on the SWCNTs ropes, they obtained the deflection
versus applied force data. Young's modulus and shear modulus were
calculated based on these measurements. The results for several
ropes at varying diameters and suspended lengths are presented.
As an example, a rope of SWCNTs with a diameter of 4.5 nm and a
length of 180 nm exhibits a value of 503 GPa and 6.5 GPa for Young's
modulus and shear modulus, respectively. Also, a rope of SWCNTs
with a diameter of 20 nm and a length of 370 nm exhibits a value of
67 and 0.7 GPa for Young's modulus and shear modulus, respectively.
This means that the mechanical properties of the CNTs ropes
enhance with smaller diameter and shorter length of the nanotubes.
The mechanical properties of CNTs appear largely independent on
their chiarality. Mechanical properties differ significantly between
SWCNTs and MWCNTs. Palaci
et al
. [70] reported that the radial
Young's modulus of MWCNTs strongly decreases with increasing
radius. In fact, external radii of about 2 nm exhibits a Young's
modulus of about 400
et al
±
200 GPa, dropping of to an asymptotic value
an order of magnitude lower at 30
10 GPa for external radii 4 nm
or greater. Additionally, Young's modulus of SWCNTs was reported
as high as 1 TPa by Dujardin
±
. [71]. Also, Young's modulus of
MWCNTs was reported as high as 1.28 TPa by Hernandez
et al
. [72].
The maximum tensile strength is reported as high as 100 GPa [73].
Because of their large tensile modulus (about 1 TPa), CNTs have
often been discussed as potential target components of nanoscale
fiber-reinforced composites for mechanical applications. Andrews
et al
et al
. [74] found that using a 5% loading of SWCNTs, the resulting
nanotube composite carbon fibers increased tensile strength by 90%
and modulus by 150%. A comprehensive overview of the mechanical
properties of the CNTs has been reported by Yakobson
. [75]
with emphasis at fundamental properties, computational models,
and fracture mechanisms; and by Mahar
et al
. [76] with emphasis at
applications in physical and chemical sensors.
et al
