In the past decades, nanostructured materials have opened new and fascinating avenues for research. Nanopolycrystalline solids, which consist of nano-sized crystalline grains and significant volume fractions of amorphous grain boundaries, are believed to have substantially different response to the thermal-mechanical-electric-magnetic loads, as compared to the response of single-crystalline materials. Nanopolycrystalline materials are expected to play a key role in the next generation of smart materials.
This research presents a framework (1) to generate full atomistic models, (2) to perform non-equilibrium molecular dynamics simulations, and (3) to study multi-physics phenomena of nanopolycrystalline solids. This work starts the physical model and mathematical representation with the framework of molecular dynamics. In addition to the latest theories and techniques of molecular dynamics simulations, this work implemented principle of objectivity and incorporates multi-physics features. Further, a database of empirical interatomic potentials is established and the combination scheme for potentials is revisited, which enables investigation of a broad spectrum of chemical elements (as in periodic table) and compounds (such as rocksalt, perovskite, wurtzite, diamond, etc.). The configurational model of nanopolycrystalline solids consists of two spatial components: (1) crystalline grains, which can be obtained through crystal structure optimization, and (2) amorphous grain boundaries, which can be obtained through amorphization process. Therefore, multi-grain multi-phase nanopolycrystalline material system can be constructed by partitioning the space for grains, followed by filling the inter-grain space with amorphous grain boundaries.
Computational simulations are performed on several representative crystalline materials and their mixture, such as rocksalt, perovskite and diamond. Problems of relaxation, mechanical loading, thermal stability, heat conduction, electrical field response, magnetic field response are studied. The simulation results of the mechanical, thermal, electrical and magnetic properties are expected to facilitate the rational design and application of nanostructured materials.
|Advisor:||Lee, James, Eskandarian, Azim|
|Commitee:||Chen, James, LeBlanc, Saniya, Leng, Yongsheng, Plesniak, Michael W.|
|School:||The George Washington University|
|Department:||Mechanical and Aerospace Engineering|
|School Location:||United States -- District of Columbia|
|Source:||DAI-B 76/06(E), Dissertation Abstracts International|
|Subjects:||Mechanics, Nanoscience, Materials science|
|Keywords:||Interatomic potentials, Molecular dynamics, Multi-physics simulation, Nanopolycrystal, Principle of objectivity|
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