Atomic Scale Simulations of Tensile Failure in Metal Oxides

1994 ◽  
Vol 357 ◽  
Author(s):  
F. H. Streitz ◽  
J. W. Mintmire
Keyword(s):  
Charge Transfer ◽  
Metal Oxides ◽  
Yield Stress ◽  
Tensile Load ◽  
Computational Method ◽  
Atomic Scale ◽  
Tensile Failure ◽  
Metallic Aluminum ◽  
Theoretical Limit ◽  
Empirical Potential

AbstractWe describe atomic-scale simulations of the failure under tensile load of an aluminum-alumina heterostructure, comparing the results with similar simulations of failure in metallic aluminum and the ceramic α-alumina. The simulations were performed using a novel computational method which explicitly includes variable charge transfer between cations and anions in an empirical potential. From our simulations we estimate the theoretical limit of yield stress for the interface to be approximately 2 GPa, at a strain of only a few percent. The theoretical limit for yield stress in α-alumina, for comparison, is about 45 GPa.

Atomic-Scale Simulations of Structural Properties of Ceramics

1996 ◽  
Vol 453 ◽  
Author(s):  
D. J. Keffer ◽  
F. H. Streitz ◽  
J. W. Mintmire
Keyword(s):  
Molecular Dynamics ◽  
Charge Transfer ◽  
Structural Properties ◽  
Computational Method ◽  
Atomic Scale ◽  
Tensile Failure ◽  
Oxide Ceramics ◽  
Ceramic Substrates ◽  
Anions And Cations ◽  
Dynamics Simulations

AbstractWe have recently developed a novel computational method for molecular dynamics simulations of metal oxide ceramics. This approach explicitly includes variable charge transfer between anions and cations. This method has been used to model the structural properties of bulk and surface alumina and aluminum systems including tensile failure of the bulk systems, as well as to model the rupture under tensile stress of an interface between a (0001) face of a-alumina and a (111) face of aluminum. We have applied this method to perform atomic-scale simulations of nanoindentation of ceramic and model rigid tips onto metal and ceramic substrates.

scholarly journals Quantum Calculations on Ion Channels: Why Are They More Useful Than Classical Calculations, and for Which Processes Are They Essential?

Symmetry ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 655
Author(s):  
Alisher M. Kariev ◽  
Michael E. Green
Keyword(s):  
Charge Transfer ◽  
Ion Channels ◽  
Correlation Energy ◽  
Force Fields ◽  
Critical Role ◽  
Atomic Scale ◽  
Quantum Calculations ◽  
Interatomic Distances ◽  
Classical Analogue ◽  
Exchange And Correlation

There are reasons to consider quantum calculations to be necessary for ion channels, for two types of reasons. The calculations must account for charge transfer, and the possible switching of hydrogen bonds, which are very difficult with classical force fields. Without understanding charge transfer and hydrogen bonding in detail, the channel cannot be understood. Thus, although classical approximations to the correct force fields are possible, they are unable to reproduce at least some details of the behavior of a system that has atomic scale. However, there is a second class of effects that is essentially quantum mechanical. There are two types of such phenomena: exchange and correlation energies, which have no classical analogues, and tunneling. Tunneling, an intrinsically quantum phenomenon, may well play a critical role in initiating a proton cascade critical to gating. As there is no classical analogue of tunneling, this cannot be approximated classically. Finally, there are energy terms, exchange and correlation energy, whose values can be approximated classically, but these approximations must be subsumed within classical terms, and as a result, will not have the correct dependence on interatomic distances. Charge transfer, and tunneling, require quantum calculations for ion channels. Some results of quantum calculations are shown.

scholarly journals Tensile Strength and Failure Types of Direct and Indirect Resin Composite Copings for Perio-Overdentures Luted Using Different Adhesive Cementation Modalities

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3517
Author(s):  
Raffaele Cesca ◽  
Vera Colombo ◽  
Bruna Ernst ◽  
Luigi Maria Gallo ◽  
Mutlu Özcan
Keyword(s):  
Resin Composite ◽  
Periodontal Diseases ◽  
Tensile Load ◽  
Resin Cement ◽  
Tensile Failure ◽  
Human Teeth ◽  
Abutment Teeth ◽  
Adhesive Cementation ◽  
To Receive ◽  
Two Parameter

Perio-overdenture design helps to reduce periodontal diseases and secondary caries on abutment teeth. Composite copings can be cemented adhesively to the abutment teeth with different techniques. In this study, direct/indirect resin composite copings for perio-overdentures, luted using different adhesive cementation modalities were compared. Human teeth (N = 40) were prepared to receive spherical attachment copings and randomly divided into four groups: (1) resin-composite copings bonded directly (DC), (2) composite copings made indirectly, luted with dual-polymerized resin cement (ICV), (3) composite copings made indirectly, bonded with resin composite (ICT), (4) composite copings made indirectly, bonded with resin composite after the immediate dentin sealing method (IDS). Specimens were tested for tensile failure and one-way ANOVA (alpha = 0.05) was performed and the two-parameter Weibull modulus, scale (m) and shape (0) were calculated. Mean tensile load (N) was significantly higher for Group IDS (238 ± 81) than for the other groups (144 ± 53–184 ± 46) (p < 0.05). Group IDS (0.54 ± 0.25 mm) showed significantly higher deformation (mm) than other groups (0.2 ± 0.1–0.32 ± 0.15) (p < 0.05). Weibull distribution presented lower shape (0) for DC (3.33) compared to other groups (3.57–4.99). Cohesive coping failures were more frequent in Group IDS (60%) and mixed failures in other groups (40–60%). In conclusion, IDS copings could be preferred over other fabrication and adhesion modalities.

scholarly journals Atomic-scale determination of spontaneous magnetic reversal in oxide heterostructures

2019 ◽  
Vol 116 (21) ◽  
pp. 10309-10316 ◽  
Author(s):  
M. Saghayezhian ◽  
Summayya Kouser ◽  
Zhen Wang ◽  
Hangwen Guo ◽  
Rongying Jin ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Charge Transfer ◽  
Oxidation State ◽  
Density Functional ◽  
Magnetic Hysteresis ◽  
Atomic Scale ◽  
Oxidation States ◽  
Internal Electric Field ◽  
Magnetic Reversal ◽  
State Changes

Interfaces between transition metal oxides are known to exhibit emerging electronic and magnetic properties. Here we report intriguing magnetic phenomena for La2/3Sr1/3MnO3 films on an SrTiO3 (001) substrate (LSMO/STO), where the interface governs the macroscopic properties of the entire monolithic thin film. The interface is characterized on the atomic level utilizing scanning transmission electron microscopy and electron energy loss spectroscopy (STEM-EELS), and density functional theory (DFT) is employed to elucidate the physics. STEM-EELS reveals mixed interfacial stoichiometry, subtle lattice distortions, and oxidation-state changes. Magnetic measurements combined with DFT calculations demonstrate that a unique form of antiferromagnetic exchange coupling appears at the interface, generating a novel exchange spring-type interaction that results in a remarkable spontaneous magnetic reversal of the entire ferromagnetic film, and an inverted magnetic hysteresis, persisting above room temperature. Formal oxidation states derived from electron spectroscopy data expose the fact that interfacial oxidation states are not consistent with nominal charge counting. The present work demonstrates the necessity of atomically resolved electron microscopy and spectroscopy for interface studies. Theory demonstrates that interfacial nonstoichiometry is an essential ingredient, responsible for the observed physical properties. The DFT-calculated electrostatic potential is flat in both the LSMO and STO sides (no internal electric field) for both Sr-rich and stoichiometric interfaces, while the DFT-calculated charge density reveals no charge transfer/accumulation at the interface, indicating that oxidation-state changes do not necessarily reflect charge transfer and that the concept of polar mismatch is not applicable in metal−insulator polar−nonpolar interfaces.

scholarly journals An Improved Numerical Simulation Approach for the Failure of Rock Bolts Subjected to Tensile Load in Deep Roadway

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-21
Author(s):  
Rui Wang ◽  
Jian-biao Bai ◽  
Shuai Yan ◽  
Yuan-ba Song ◽  
Guang-dong Wang
Keyword(s):  
Numerical Simulation ◽  
Tensile Load ◽  
Elongation Rate ◽  
Original Model ◽  
Rock Bolt ◽  
Tensile Failure ◽  
Simulation Approach ◽  
Rock Bolts ◽  
Modified Model ◽  
Free Section

Our goal was to develop an effective research tool for roadways with significant deformations supported by rock bolts. The improved numerical simulation approach is constructed through additional development of FLAC3D. The aim is to modify the shortcoming that the original model in FLAC3D regards the plastic tensile strain of any arbitrary rock bolt element node as the rupture discrimination criterion. The FISH programming language is adopted to conduct the secondary development and to embed the revised model into the main program of FLAC3D. Taking an actual mining roadway as the simulation object, two simulation schemes adopting the newly improved approach and the original method were conducted, respectively. The results show that (1) the PILE element that constitutes the rock bolt-free section with the maximum elongation rate ruptures after modification, while the rock bolt tendon elongation rate reaches beyond the predefined tensile rupture elongation rate; (2) the modified model in which the rock bolt is mainly subjected to tension realises the tensile rupture phenomenon at the end of the rock bolt-free section and the rock bolt at the junction between the free section and the anchoring section; and (3) only four rock bolts that are in the roadway sides showed rupture in the modified model, and all rock bolts showed rupture in the original model. The tensile failure of the rock bolt led that the modified model scheme is closer to the actual. Compared with the modified model, in the original model, deformation of the surrounding rock masses is severe. This is resulted by the rupture of all rock bolts in the original model. The analysis shows that the improved numerical simulation approach is much more reliable for large deformation roadway behavior with rock bolt support.

A nanocomposite superstructure of metal oxides with effective charge transfer interfaces

2014 ◽  
Vol 5 (1) ◽  
Author(s):  
Zhenfeng Bian ◽  
Takashi Tachikawa ◽  
Peng Zhang ◽  
Mamoru Fujitsuka ◽  
Tetsuro Majima
Keyword(s):  
Charge Transfer ◽  
Metal Oxides ◽  
Effective Charge ◽  
Effective Charge Transfer
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