Biomedical Engineering Reference
In-Depth Information
Figure 7.5
Relationship between bending strength (left) or fracture
toughness (right) and volume fraction of HA in HA-Ti
microcrystalline material [4].
For both nanocomposite and microcomposite materials,
Young's modulus changed corresponding to the relative density.
Both bending strength and fracture toughness are sensitive to
the microstructure of the materials. They are associated with the
coniguration and distribution of the constitutional phases and
the pores in the materials. The pores reduce the effective area
bearing the load and can result in the stress concentration in the
composites. Consequently, bending strength and fracture toughness
of the composites decrease sharply according to the approximately
exponential relation with the increase of the porosity.
The bending strength and fracture toughness of pure HA (37
MPa and 0.66 MPa·m
1/2
) are far lower than those of pure Ti (972
MPa and 30 MPa·m
1/2
). For this reason, the effect of HA phase on
the bending strength and fracture toughness of Ti-HA composites
is similar to the one of pores in Ti-matrix of the composite. Thus
the sharp decrease of bending strength and fracture toughness of
Ti-20 vol% HA composite to only about 170 MPa and 3.57 MPa·m
1/2
,
respectively, and can be contributed to the existence of 20% HA
phase and the porosity of 2.1%.
It should be mentioned that bending
strength and fracture toughness of compact human bond for load-
bearing applications can reach about 130 MPa and 2 MPa·m
1/2
,
respectively. Thus, Ti-20 vol% HA composite, with higher bending
strength and fracture toughness than the compact human bone,
is suitable for load-bearing applications from the point of view of
mechanical properties [7].
Both nano- and microcomposites have a lower Young's modulus
as compared to titanium. From the perspective of future application
of this type of composites as biomaterials for heavy load-bearing
