Biomedical Engineering Reference
In-Depth Information
Table 8.4
Candidate fillers
Material
E
(GPa)
σ (MPa)
E
f
/
E
a
Fibers
Graphite (high
E
)
577
1725
192
Tungsten
400
4000
133
Alumina
380
1725
126
Zirconia
345
2050
125
250
2350
83
Graphite (high σ)
316L stainless steel
193
1000
64
Polyaramid (high
E
)
131
3800
45
Ti6AI4V
115
930
38
Titanium
115
280
38
S-glass
b
86
4500
29
Aluminum
73
90
24
E-glass
c
72
3500
24
Polyaramid (low
E
)
62
3800
21
Whiskers
Carbon
980
21,000
327
Silicon carbide
840
11,000
280
Boron carbide
483
13,800
161
Alumina
429
20,700
142
Titania (alpha rutile)
380
4000
127
Silicon nitride
379
13,800
126
Aluminum nitride
320
5000
107
Note:
Values are generic (in tension); actual individual materials may vary sig-
nificantly in properties.
E
m
= 3 GPa.
a
Composition: SiO
2
, Al
2
O
3
, CaO; balance, 52-56:12-16:16-25:balance.
b
Composition: SiO
2
, A1
2
O
3
, MgO; balance, 65:25:10:trace.
c
are being considered for design of PMCs for orthopaedic applications.
Table 8.3 includes typical values of flexural stiffness and strength with a
30% glass fiber fill for comparison. Note in Table 8.4 that whiskers have
significantly higher values of tensile strength and stiffness than fibers.
This is due to the relatively defect-free nature of whiskers; however, they
are, in general, extremely brittle.
PMC fabrication
PMCs may be distinguished with respect to processing by whether their
fillers are particulate (grain, whisker, short fiber, etc.) or continuous.
PMCs with particulate fillers are fabricated in much the same way that
polymeric components are (Figure 8.1; see also Figure 6.6), depending
on whether the matrix is a thermoset or a thermoplastic. Three addi-
tional problems arise from the addition of the filler:
1. The fluid matrix must be able to “wet” the filler, that is, to form a
stable phase interface. Matrix-filler combinations that do not meet
this requirement will produce only extremely weak PMCs.
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