Biomedical Engineering Reference
In-Depth Information
700
BASF G30-500
Toho HTA
600
M60J
T50
IM 6
IM 8
GY-70
500
IM 43-750
M50J
M46
HM
st
M40J
400
M40
HMS4
300
T650/42
T800H
T40
200
T700S
AMOCO T300
T1000
100
34-700
Fortafil
'121'
Grafil XA
Hexcel AS4C
0
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
Tensile Strength (GPa)
Figure 3.5
Tensile strength and modulus of a range of commercial carbon fibers. Source: Invibio.
regions toward the ends of the fibers, particularly for
those fibers that are more highly aligned parallel to
the applied load. This applied load acts through the
interface to load the fiber in tension. A weak fiber/
matrix interface (with low shear strength) would
mean that fibers would likely de-bond from the
matrix at low applied stress and in this case the
material would be relatively weakened and the fibers
would be relatively inefficient at reinforcing the
polymer. A strong interface between fiber and
matrix allows for more efficient fiber utilization,
meaning that a greater proportion of each fiber is
capable of sustaining load.
Figure 3.7
is an electron micrograph of a PEEK/
short carbon fiber fracture surface showing PEEK
polymer matrix adhering to carbon fibers after
a tensile test. This clearly illustrates that in the case
of carbon fibers and PEEK there is a strong interfa-
cial bond between the two components, because
a weak interface would have resulted in “clean
fibers” without any adhering PEEK polymer. A low
interfacial strength can be problematic with regard to
materials' performance in the application. Indeed,
the dangers of using materials that are substantially
incompatible at the microscale of the interface can be
illustrated with reference to the ill-fated development
of carbon fiber-filled UHMWPE in tibial bearing
components.
Carbon fiber-reinforced polyethylene, coupled
with a smooth cobalt chrome alloy counterpart, was
Figure 3.6
Relative wear performance of polymer
against cobalt chrome and ceramic for prosthetic hip.
Source: Invibio.
Figure 3.7
Electron micrograph of fractured short fiber
reinforced PEEK compound illustrating adhered matrix
on fibers and a strong fiber/matrix interfacial bond.