1,890 research outputs found
A parallel computing-visualization framework for polycrystalline minerals
In this report, we have reported some preliminary results in the development of a parallel computing-visualization framework for large-scale molecular dynamics simulations of polycrystals of minerals, which are geophysically relevant for Earth’s mantle. First, we have generated the input configurations of atoms belonging to various grains distributed in the space in a way, which resembles the polycrystalline structure of the minerals. The Input configuration is developed using Voronoi geometry. Thus generated polycrystalline system is simulated using the PolyCrystal Molecular Dynamics algorithm. Performance tests conducted using up to 256 processors and a couple of millions of atoms have shown that the computation time per MD step remains under 20 seconds. The other important part is the development of an efficient visualization system to interactively explore the massive three dimensional and time-dependent datasets produced by MD simulations. Some results are presented for the simulation of two-grain structure. The proposed framework is expected to be useful in simulations of more realistic and complex rheological (mechanical) properties of important Earth forming mineral phases under different conditions of stresses and temperatures
Phase Stability and Thermoelectric Properties of the Mineral FeS2: An Ab Initio Study
First principles calculations were carried out to study the phase stability
and thermoelectric properties of the naturally occurring marcasite phase of
FeS at ambient condition as well as under pressure. Two distinct density
functional approaches has been used to investigate the above mentioned
properties. The plane wave pseudopotential approach was used to study the phase
stability and structural, elastic, and vibrational properties. The full
potential linear augment plane wave method has been used to study the
electronic structure and thermoelectric properties. From the total energy
calculations, it is clearly seen that marcasite FeS is stable at ambient
conditions, and it undergoes a first order phase transition to pyrite FeS
at around 3.7 GPa with a volume collapse of about 3. The calculated ground
state properties such as lattice parameters, bond lengths and bulk modulus of
marcasite FeS agree quite well with the experiment. Apart from the above
studies, phonon dispersion curves unambiguously indicate that marcasite phase
is stable under ambient conditions. Further, we do not observe any phonon
softening across the marcasite to pyrite transition and the possible reason
driving the transition is also analyzed in the present study, which has not
been attempted earlier. In addition, we have also calculated the electronic
structure and thermoelectric properties of the both marcasite and pyrite
FeS. We find a high thermopower for both the phases, especially with p-type
doping, which enables us to predict that FeS might find promising
applications as good thermoelectric materials.Comment: 10 Figure
Review of the Synergies Between Computational Modeling and Experimental Characterization of Materials Across Length Scales
With the increasing interplay between experimental and computational
approaches at multiple length scales, new research directions are emerging in
materials science and computational mechanics. Such cooperative interactions
find many applications in the development, characterization and design of
complex material systems. This manuscript provides a broad and comprehensive
overview of recent trends where predictive modeling capabilities are developed
in conjunction with experiments and advanced characterization to gain a greater
insight into structure-properties relationships and study various physical
phenomena and mechanisms. The focus of this review is on the intersections of
multiscale materials experiments and modeling relevant to the materials
mechanics community. After a general discussion on the perspective from various
communities, the article focuses on the latest experimental and theoretical
opportunities. Emphasis is given to the role of experiments in multiscale
models, including insights into how computations can be used as discovery tools
for materials engineering, rather than to "simply" support experimental work.
This is illustrated by examples from several application areas on structural
materials. This manuscript ends with a discussion on some problems and open
scientific questions that are being explored in order to advance this
relatively new field of research.Comment: 25 pages, 11 figures, review article accepted for publication in J.
Mater. Sc
Grain coarsening in two-dimensional phase-field models with an orientation field
In the literature, contradictory results have been published regarding the
form of the limiting (long-time) grain size distribution (LGSD) that
characterizes the late stage grain coarsening in two-dimensional and
quasi-two-dimensional polycrystalline systems. While experiments and the
phase-field crystal (PFC) model (a simple dynamical density functional theory)
indicate a lognormal distribution, other works including theoretical studies
based on conventional phase-field simulations that rely on coarse grained
fields, like the multi-phase-field (MPF) and orientation field (OF) models,
yield significantly different distributions. In a recent work, we have shown
that the coarse grained phase-field models (whether MPF or OF) yield very
similar limiting size distributions that seem to differ from the theoretical
predictions. Herein, we revisit this problem, and demonstrate in the case of OF
models [by R. Kobayashi et al., Physica D 140, 141 (2000) and H. Henry et al.
Phys. Rev. B 86, 054117 (2012)] that an insufficient resolution of the small
angle grain boundaries leads to a lognormal distribution close to those seen in
the experiments and the molecular scale PFC simulations. Our work indicates,
furthermore, that the LGSD is critically sensitive to the details of the
evaluation process, and raises the possibility that the differences among the
LGSD results from different sources may originate from differences in the
detection of small angle grain boundaries
Torsional properties of bamboo-like structured Cu nanowires
Recently, researchers reported that nanowires (NWs) are often polycrystalline, which contain grain or twin boundaries that transect the whole NW normal to its axial direction into a bamboo like structure. In this work, large-scale molecular dynamics simulation is employed to investigate the torsional behaviours of bamboo-like structured Cu NWs. The existence of grain boundaries is found to induce a considerably large reduction to the critical angle, and the more of grain boundaries the less reduction appears, whereas, the presence of twin boundaries only results in a relatively smaller reduction to the critical angle. The introduction of grain boundaries reduces the torsional rigidity of the NW, whereas, the twin boundaries exert insignificant influence to the torsional rigidity. NWs with grain boundaries are inclined to produce a local HCP structure during loading, and the plastic deformation is usually evenly distributed along the axial axis of the NW. The plastic deformation of both perfect NW and NWs with twin boundaries is dominated by the nucleation and propagation of parallel intrinsic stacking faults. This study will enrich the current understanding of the mechanical properties of NWs, which will eventually shed lights on their applications
Predicting the Mechanical Properties of Nanocomposites Reinforced with 1-D, 2-D and 3-D Nanomaterials
Materials with features at the nanoscale can provide unique mechanical properties and increased functionality when included as part of a nanocomposite. This dissertation utilizes computational methods at multiple scales, including molecular dynamics (MD) and density functional theory (DFT), and the coupled atomistic and discrete dislocation multiscale method (CADD), to predict the mechanical properties of nanocomposites possessing nanomaterials that are either 1-D (carbyne chains), 2-D (graphene sheets), or 3-D (Al/amorphous-Si core-shell nanorod).
The MD method is used to model Ni-graphene nanocomposites. The strength of a Ni-graphene nanocomposite is found to improve by increasing the gap between the graphene sheet and a crack embedded in the Ni matrix. Ni-graphene nanocomposites also show substantially greater strength than pure Ni, depending on the loading direction and crack orientation relative to the graphene sheet. Moreover, polycrystalline graphene may serve as a better reinforce in Ni-graphene nanocomposites due to its improved interfacial shear stress with the Ni matrix compared to pristine graphene. This work develops a patchwork quilt method for generating polycrystalline graphene sheets for use in MD models.
Carbyne-based nanocomposites are modeled from first principles using DFT. This research finds that carbyne can only serve as an effective reinforcement in Ni-based nanocomposites when it is dielectrically screened from the Ni matrix, otherwise the carbyne structure is lost. When graphene is used as a dielectric screen, the local stiffness of the nanocomposite improves with the number of carbyne chains present. Specific stiffness is introduced as an alternative to elastic stiffness for characterizing low-dimensional materials because it is not dependent on volume when derived using an energy vs. strain relation.
A two-material formulation of CADD is developed to model Al/a-Si core-shell nanorods under indentation/retraction. The structural deformation behavior is found to be dependent on the geometry of both core and shell. When present, the a-Si shell protects the Al core by delocalizing forces produced by the indenter. It is also found that substrate deformation becomes important for core-shell structures with sufficiently small cores.
This work can help guide experimental and computational work related to the discussed 1-D, 2-D and 3-D nanomaterials and aid in future nanocomposite design
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