Biomedical Engineering Reference
In-Depth Information
thermal conductivity of a composite can be calculated (Nan et al., 2003):
2
K
c
¼
K
m
þ
K
f
cos
y
V
f
½
7
:
6
where K
m
and K
f
are the thermal conductivities of the matrix and fibers,
respectively, V
f
is the fiber volume and
is the angle between fiber axis and
the given direction. For aligned and random orientation of fibers, cos
2
θ
is 1
and 1/3, respectively (Nan et al., 2003). The calculated value of the thermal
conductivity of CNT-glass/glass-ceramic matrix composites obtained from
equation 7.6 is generally two orders of magnitude higher than the
experimental value. The thermal resistance due to large interfacial surface
area between CNTs and glass matrix is the most likely reason for the
reduced increment of thermal conductivity of composites. An expression to
calculate thermal conductivity of composites incorporating interfacial
thermal resistance is available and has proven quite widely applicable
(Nan et al., 2004):
θ
K
f
L
2R
i
K
f
þ
2
K
c
¼
K
m
þ
L
cos
y
V
f
½
7
:
7
where L is the length of fibers and R
i
is the interfacial thermal resistance,
also known as Kapitza resistance.
7.6.4 Technological properties
A variety of technological properties of CNT-glass/glass-ceramic matrix
composites are particularly relevant to potential industrial applications.
Recently, a model system based on CNT-SiO
2
composites has been used to
explore such properties, including wear and friction resistance and thermal
shock, cycling and ageing resistance, as now discussed (Subhani, 2012b).
Wear and friction resistance
No published data on the wear and friction properties of CNT-glass/glass-
ceramic composites are available, although related studies on CNT-ceramic
composites have been performed (Ahmad et al., 2010, An et al., 2003)
showing a decrease in wear rate at low CNT loadings (
<
5wt%) but an
increase at higher CNT contents, as observed with many primary mechanical
properties (Ahmad et al., 2010). Wear and friction experiments on CNT-
glass/glass-ceramic composites can be performed by different methods;
commonly available techniques are the ball-on-disk and pin-on-disk tests, in
which a ball or a pin of a hard material slides under pressure against the flat
surface of the composite specimen. A variety of materials ranging from
hardened steels to ceramics and different sizes (diameters) of pins and balls are
