Biomedical Engineering Reference
In-Depth Information
out to investigate the different properties and possible applications of this
material.
The majority of interatomic potentials developed for SiC material system
focus on describing the material properties of
-SiC [e.g. 64-68]. We choose
Tersoff's bond order potential to model interatomic interactions in SiC. At
the interface of SiC and Si
3
N
4
, we need to be able to describe Si-C, Si-Si, C-
N, and Si-N interactions. Tersoff's potential is useful only for describing the
bulk Si-Si, C-C, and Si-C interactions [69]. Accordingly, a pair potential
form similar to that used for Si
3
N
4
is sought to be used for interfacial
interactions at the SiC-Si
3
N
4
interfaces. We use the of potentials Marian
et al. [70] to describe Si-N, Si-Si interactions, the potential of Vincent and
Merz [71] to describe C-N interactions, and the potential of Jian et al. [72] to
describe Si-C interactions at the SiC-Si
3
N
4
interfaces.
β
5.5.2 High-performance computing and mechanical
deformation algorithm for MD simulations
MD simulations are performed using a modified version of a scalable
parallel code, DL_POLY 2.14 [73, 74]. Electrostatic calculations using the
code can be carried out for charged as well as neutral systems using well-
established algorithms [e.g. 75-77]. The code has been modified and tested
on a system of 1 000 000 atoms for a model ceramic matrix composite (Al
+Fe
2
O
3
) material system and is benchmarked for scalable high-perfor-
mance classical MD simulations for large atomic ensembles with millions of
atoms [73, 78].
The simulations primarily focus on obtaining virial stress versus strain
relations and visual atomistic deformation information in order to delineate
the deformation mechanisms. In previous uniaxial quasistatic deformation
analyses of nanocrystalline Cu by Schiøtz et al. [79], strain was calculated by
recording the changes in positions of individual atoms. The average virial
stress was calculated at every step in order to obtain the stress-strain
relations. A modified version of this approach is used here. An alternative
method to obtain uniaxial stress-strain curves is to record strain-time
curves at several values of applied stress and then deduce the stress-strain
relations [80]. Spearot et al. [81] used both methods and found that the
modified method [82] works better because it controls the applied strain and
closely emulates controlled displacement experiments. The modifications to
the method of Schiøtz et al. [79] include the use of a combination of the
algorithms for NPT and NVT ensembles. Alternating steps of stretching and
equilibration at constant temperature are carried out to approximate
uniaxial quasistatic deformation. Initially, the system is equilibrated at a
specified temperature (300K). During equilibration, NVT equations of
