Using a self-consistent linear combination of atomic orbitals method based on density-functional theory in a local-density approximation, the electronic structure in the high-temperature ceramics α−Si3N4 and β−Si3N4...
Using a self-consistent linear combination of atomic orbitals method based on density-functional theory in a local-density approximation, the electronic structure in the high-temperature ceramics α−Si3N4 and β−Si3N4 and at the Si(111)/Si3N4(001) interface have been calculated. The resulting charge transfer suggests that the ionic formula can be written as Si3+1.24N4−0.93. For the Si(111)/Si3N4(001) interface, the silicon atoms from the silicon side lose some electrons to the nitrogen atoms of the silicon nitride side forming Si-N bonds at the interface. The calculated electronic density of states spectrum of Si 2p core levels for this interface is in good agreement with x-ray photoemission spectroscopy experiments.
Million atom molecular-dynamics simulations are performed to investigate the structure, dynamics, and mechanical behavior of cluster-assembled Si3N4. These solids contain highly disordered interfacial regions with 50%...
Million atom molecular-dynamics simulations are performed to investigate the structure, dynamics, and mechanical behavior of cluster-assembled Si3N4. These solids contain highly disordered interfacial regions with 50% undercoordinated atoms. Systems sintered at low pressures have percolating pores whose surface morphologies are well characterized by two values of the roughness exponent, 0.46 and 0.86; these are close to the experimental values found by Bouchaud et al. for fracture surfaces. Results for elastic moduli are consistent with a three-phase model for heterogeneous materials.
Using 106-atom molecular-dynamics simulations, we investigate dynamic fracture in nanophase Si3N4. The simulations reveal that intercluster regions are amorphous, and they deflect cracks and give rise to local crack b...
Using 106-atom molecular-dynamics simulations, we investigate dynamic fracture in nanophase Si3N4. The simulations reveal that intercluster regions are amorphous, and they deflect cracks and give rise to local crack branching. As a result, the nanophase system is able to sustain an order-of-magnitude larger external strain than crystalline Si3N4. We also determine the morphology of fracture surfaces: For in-plane fracture surface profiles the roughness exponent ζ=0.57 and for out-of-plane profiles the exponents ζ⊥=0.84 and ζ‖=0.75 are in excellent agreement with experiments.
Crack propagation in a graphite sheet is investigated with million atom molecular-dynamics simulations based on Brenner's reactive empirical bond-order potential. For certain crystalline orientations, multiple cra...
Crack propagation in a graphite sheet is investigated with million atom molecular-dynamics simulations based on Brenner's reactive empirical bond-order potential. For certain crystalline orientations, multiple crack branches with nearly equal spacing sprout as the crack tip reaches a critical speed of 0.6VR, where VR is the Rayleigh wave speed. This results in a fracture surface with secondary branches and overhangs. Within the same branch the crack-front profile is characterized by a roughness exponent, α=0.41±0.05. However, for interbranch fracture surface profiles the return probability yields α=0.71±0.10. Fracture toughness is estimated from Griffith analysis and local-stress distributions.
Million-atom molecular-dynamics (MD) simulations are performed to study the structure, mechanical properties, and dynamic fracture in nanophase Si3N4. We find that intercluster regions are highly disordered: 50% of Si...
Million-atom molecular-dynamics (MD) simulations are performed to study the structure, mechanical properties, and dynamic fracture in nanophase Si3N4. We find that intercluster regions are highly disordered: 50% of Si atoms in intercluster regions are three-fold coordinated. Elastic moduli of nanophase Si3N4 as a function of grain size and porosity are well described by a multiphase model for heterogeneous materials. The study of fracture in the nanophase Si3N4 reveals that the system can sustain an order-of-magnitude larger external load than crystalline Si3N4. This is due to branching and pinning of the crack front by nanoscale microstructures.
New multiscale algorithms and a load-balancing scheme are combined for molecular-dynamics simulations of nanocluster-assembled ceramics on parallel computers. Million-atom simulations of the dynamic fracture in nanoph...
New multiscale algorithms and a load-balancing scheme are combined for molecular-dynamics simulations of nanocluster-assembled ceramics on parallel computers. Million-atom simulations of the dynamic fracture in nanophase silicon nitride reveal anisotropie self-affine structures and crossover phenomena associated with fracture surfaces.
Dynamics of amorphization and fracture in SiSe2 nanowires are studied using the molecular-dynamics method. We find that fracture is initiated in an amorphous region at the nanowire surface. Local amorphization propaga...
Dynamics of amorphization and fracture in SiSe2 nanowires are studied using the molecular-dynamics method. We find that fracture is initiated in an amorphous region at the nanowire surface. Local amorphization propagates across the nanowire while multiple cracks start at the boundaries of the amorphous region. Results for the time evolution of amorphization, crack propagation, and fracture are discussed.
Fracture in amorphous silica is studied using million-atom molecular dynamics simulations. The dynamics of crack propagation, internal stress fields, and the morphology of fracture surfaces are examined as a function ...
Fracture in amorphous silica is studied using million-atom molecular dynamics simulations. The dynamics of crack propagation, internal stress fields, and the morphology of fracture surfaces are examined as a function of temperature and strain rate. At 300K and 600K we observe brittle fracture: internal stress increases to a critical value (typically 2 - 3 GPa) and then turns over when the crack reaches a terminal speed on the order of half the Rayleigh wave speed. At 900K crack propagation slows down dramatically due to plastic deformation and the material becomes ductile.
Crack propagation in amorphous Si3N4 films is investigated with large-scale molecular-dynamics simulations on parallel machines. We observe a correlation between the speed of crack propagation and the morphology of fr...
Crack propagation in amorphous Si3N4 films is investigated with large-scale molecular-dynamics simulations on parallel machines. We observe a correlation between the speed of crack propagation and the morphology of fracture surfaces. Initially, as the crack propagates slowly, the roughness exponent for fracture surfaces is found to be 0.44. However, beyond a certain speed of crack propagation, the exponent crosses over to 0.8. This crossover behavior is similar to the recent experimental finding by Bouchaud and Navéos.
Multiresolution molecular dynamics approach on parallel computers has been used to investigate fracture in ceramic materials. In microporous silica, critical behavior at fracture is analyzed in terms of pore percolati...
Multiresolution molecular dynamics approach on parallel computers has been used to investigate fracture in ceramic materials. In microporous silica, critical behavior at fracture is analyzed in terms of pore percolation and kinetic roughening of fracture surfaces. Crack propagation in amorphous silicon nitride films is investigated, and a correlation between the speed of crack propagation and the morphology of fracture surfaces is observed. In crystalline silicon nitride films, temperature-assisted void formation in front of a crack tip slows down crack propagation.
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