Biomedical Engineering Reference
In-Depth Information
600
Beech (axial)
Poplar (axial)
Mahogany (axial)
Red oak (axial)
Sapele (axial)
(a)
500
UDP
400
300
NUDP
200
100
0
40
45
50
55
60
65
Porosity (%)
90
Beech (radial)
Poplar (radial)
Poplar (tangential)
Mahogany (radial)
Mahogany (tangential)
Red oak (radial)
Red oak (tangential)
Sapele (radial)
Sapele (tangential)
(b)
80
70
60
50
40
30
20
10
0
40
45
50
55
60
65
Porosity (%)
Figure 11.13. Compressive strength as a function of porosity for: (a) axial; and (b) tangential
and radial orientations with UDP and NUDP bioSiC grouped in the axial plot (error bars equal
one standard deviation).
Fracture toughness of porous bioSiC has a strong dependence on orientation
and on porosity, as shown in Figure 11.14. Experiments show higher fracture
toughness when cracks propagate in directions perpendicular to the axial direc-
tion and lower fracture toughness values for propagation in directions parallel to
the axial direction. This dependence of fracture toughness on crack propagation
direction can be explained by the orientation of the elongated anisotropic pores.
Cracks propagating in directions parallel to the axial direction are able to propa-
gate in preferred paths along these elongated pores. Cracks in transverse direc-
tions are forced to propagate along tortuous paths and across these elongated
pores, which results in higher fracture toughness values. The fracture toughness of
Si/SiC composites for crack propagation perpendicular to the axial direction are
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