Biomedical Engineering Reference
In-Depth Information
the absence of an interface in Si
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4
, the presence of an initial crack will lead
to higher internal stresses. The curves also show that internal stresses will
decrease with an increase in particle size and the corresponding reduction in
the interparticle spacing (owing to the imposed PBCs). The difference
between the stresses with and without initial cracks can be explained by a
significant stress concentration caused due to the presence of second-phase
particles and their interactions with the propagating initial crack. This stress
concentration reduces with an increase in particle size, leading to lower
internal stresses overall.
In the case of microstructures M5 and M6 with SiC inclusion now placed
along a Si
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interface, a reversal in trend regarding the effects of particle
size and initial crack is observed. As was observed earlier in the case of M1
and M2, the presence of a crack does not result in an appreciable stress
concentration in M5 and M6. A combined effect of the change in particle
size and the presence of an interface is now that the internal stresses rise with
an increase in particle size and a reduction in particle spacing. This result is
in direct contrast to earlier observations of a reduction in internal stresses
with increase in particle size for microstructures M3 and M4. The difference
is now the presence of the interface. The interface, while imparting higher
toughness for a given particle size, is also a site for structural discontinuity.
The presence of second-phase particles with a reduction in spacing between
the particles will lead to a stronger material when particles are present along
the interface. The trend is reversed when particles are present in the grain
interior.
Overall, the combination of observations from Figs 5.12, 5.13, and 5.14
reveals that the effect of interfaces is to strengthen the material by raising
toughness. The presence of second-phase particles will lead to a reduction in
strength. The presence of nanosized cracks in an ionic material does not
offer significant stress concentration until aided by the presence of second-
phase inclusions. The toughening of the nanocomposite in the presence of a
combination of interfaces and second-phase particles is strongly dependent
upon whether the second-phase particles are placed along interfaces or in
grain interiors. In addition, the strengthening is also dependent upon the
size and relative spacing between particles, irrespective of whether the
particles are in grain interiors or at the interfaces. The trend, however, is
different for interfaces and grain interiors.
5.7
Conclusions
This chapter has CFEM and MD based analyses to understand the effect of
second-phase SiC particles on the strength of SiC-Si
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nanocomposites.
CFEM analyses can explicitly account for the effect of nanoscale inclusions
on the strength of nanocomposites. However, the CFEM cannot account for
