Biomedical Engineering Reference
In-Depth Information
5.10 Damage distribution in (a) Class I, (b) Class II, and (c) Class III
microstructures at the loading rate of 2m/sec and time t = 0.01875
μ
sec.
Close-up insets offer higher resolution view of the damage region.
Broken particles have distorted 'crumbled' appearance. The intact
particles have near circular appearance. Corresponding fragmented GBs
show up as zigzag lines in the diffused damage region. These lines are
outlines of the fragmented GB elements.
of microstructures at time t=0.01875
μ
sec (Fig. 5.10) at V 0 =2 m/sec are
now discussed.
A concentrated stress field similar to homogeneous materials near the
propagating crack tip is seen in all three microstructures. The distribution of
stress around the crack tip is strongly affected by the distribution of second-
phase SiC particles with respect to Si 3 N 4 GBs. The presence of SiC particles
inside Si 3 N 4 grain interior in the case of Class I and Class III
microstructures results in stress concentration over and in excess of the
crack tip stresses that are seen in the case of Class II microstructure where
the SiC particles are placed solely along GBs. In the case of the Class II
microstructure, near crack tip stresses are concentrated in a very small
region. This is contrary to the case of the Class I microstructure where the
near crack tip stress fields are spread over a larger microstructural region.
Owing to the SiC particle stress concentration, intergranular microcracks
originating in the microstructure can also be seen. Stress distribution in the
Class III microstructure lies in between that of the Class I and Class II
microstructures. The effect of the difference in the fracture and bulk
properties of GBs and Si 3 N 4 matrix on stress distribution is insignificant in
comparison to the effect of the second-phase particle placement. GBs are
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