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Articles 31 - 40 of 40
Full-Text Articles in Mechanical Engineering
Molecular Dynamics Simulation Of Atomic Friction: A Review And Guide, Yalin Dong, Qunyang Li, Ashlie Martini
Molecular Dynamics Simulation Of Atomic Friction: A Review And Guide, Yalin Dong, Qunyang Li, Ashlie Martini
Dr. Yalin Dong
This paper reviews recent progress in molecular dynamics simulation of atomic-scale friction measured by an atomic force microscopy. Each section of the review focuses on an individual condition or parameter that affects atomic friction including materials, surfaces, compliance, contact area, normal load, temperature, and velocity. The role each parameter plays is described in the context of both experimental measurements and simulation predictions. In addition, the discussion includes an overview of the research community's current understanding of observed effects, guidelines for implementation of those effects in an atomistic simulation, and suggestions for future research to address open questions. Taken together, this …
The Roles Of Statics And Dynamics In Determining Transitions Between Atomic Friction Regimes, Yalin Dong, Danny Perez, Arthur Voter, Ashlie Martini
The Roles Of Statics And Dynamics In Determining Transitions Between Atomic Friction Regimes, Yalin Dong, Danny Perez, Arthur Voter, Ashlie Martini
Dr. Yalin Dong
We introduce a model AFM tip/substrate system that includes full atomistic detail as well as system compliance to study the transitions between three regimes of atomic friction: smooth sliding, stick-single slip, and stick-multiple slip. We characterize these atomic friction regimes in terms of static and dynamic effects, and investigate how the slip modes affect the mean friction. Molecular statics calculations show that reduced-order model predictions of possible transitions between slip regimes are generally adequate for a fully atomistic system, even for complex reaction coordinates. However, molecular dynamics simulations demonstrate that, while static features of the system govern possible slip regimes, …
Correlation Between Probe Shape And Atomic Friction Peaks At Graphite Step Edges, Yalin Dong, Xin Liu, Philip Egberts, Zhijiang Ye, Robert Carpick, Ashlie Martini
Correlation Between Probe Shape And Atomic Friction Peaks At Graphite Step Edges, Yalin Dong, Xin Liu, Philip Egberts, Zhijiang Ye, Robert Carpick, Ashlie Martini
Dr. Yalin Dong
Molecular dynamics simulation and atomic force microscopy are used to study the nature of friction between nanoscale tips and graphite step edges. Both techniques show that the width of the lateral force peak as the probe moves up a step is directly correlated with the size and shape of the tip. The origin of that relationship is explored and the similarities and differences between the measurements and simulations are discussed. The observations suggest that the relationship between lateral force peak width and tip geometry can be used as a real-time monitor for tip wear during atomic scale friction measurements.
Effects Of Substrate Roughness And Electron–Phonon Coupling On Thickness-Dependent Friction Of Graphene, Yalin Dong
Effects Of Substrate Roughness And Electron–Phonon Coupling On Thickness-Dependent Friction Of Graphene, Yalin Dong
Dr. Yalin Dong
Molecular dynamics simulation and the two-temperature method are carried out to model the effects of substrate roughness as well as electron–phonon coupling on thickness-dependent friction on graphene. It is found that substrate roughness can significantly enhance friction of graphene, which is orders of magnitude larger than that on smooth substrate due to puckering effect. Additionally, the adhesive force between graphene and substrate plays opposite roles for smooth and rough substrates. While on a smooth substrate, a larger adhesion hinders the wrinkle formation in graphene, therefore suppressing friction, on a rough substrate, adhesion helps induce atomic roughness in graphene and leads …
Friction, Slip And Structural Inhomogeneity Of The Buried Interface, Yalin Dong, Qunyang Li, Jingjie Wu, Ashlie Martini
Friction, Slip And Structural Inhomogeneity Of The Buried Interface, Yalin Dong, Qunyang Li, Jingjie Wu, Ashlie Martini
Dr. Yalin Dong
An atomistic model of metallic contacts using realistic interatomic potentials is used to study the connection between friction, slip and the structure of the buried interface. Incommensurability induced by misalignment and lattice mismatch is modeled with contact sizes that are large enough to observe superstructures formed by the relative orientations of the surfaces. The periodicity of the superstructures is quantitatively related to inhomogeneous shear stress distributions in the contact area, and a reduced order model is used to clarify the connection between friction and structural inhomogeneity. Finally, the movement of atoms is evaluated before, during and after slip in both …
Thermal Activation In Atomic Friction: Revisiting The Theoretical Analysis, Yalin Dong, Danny Perez, Hongyu Gao, Ashlie Martini
Thermal Activation In Atomic Friction: Revisiting The Theoretical Analysis, Yalin Dong, Danny Perez, Hongyu Gao, Ashlie Martini
Dr. Yalin Dong
The effect of thermal activation on atomic-scale friction is often described in the framework of the Prandtl–Tomlinson model. Accurate use of this model relies on parameters that describe the shape of the corrugation potential β and the transition attempt frequency f0. We show that the commonly used form of β for a sinusoidal corrugation potential can lead to underestimation of friction, and that the attempt frequency is not, as is usually assumed, a constant value, but rather varies as the energy landscape evolves. We partially resolve these issues by demonstrating that numerical results can be captured by a model with …
Effect Of Molecular Structure On Liquid Slip, Ajay Vadakkepatt, Yalin Dong, Seth Lichter, Ashlie Martini
Effect Of Molecular Structure On Liquid Slip, Ajay Vadakkepatt, Yalin Dong, Seth Lichter, Ashlie Martini
Dr. Yalin Dong
Slip behavior of three liquids with distinct molecular shapes—linear (hexadecane), branched (pentaerythritol tetra), and a chain of rings (polyphenylether)—is studied using molecular dynamics simulation and reduced-order modeling. Slip at a liquid-solid interface is shown to be affected by the molecular structure of the liquid. A two-dimensional Frenkel-Kontorova model captures the fundamental structural features of the liquid molecules and gives insight into how molecules flex and slip along the surface. We formulate an approximation to the Peierls-Nabarro energy which incorporates both the position of liquid atoms relative to substrate atoms and molecular flexibility. We find that increased molecular flexibility can lead …
Physically Representative Atomistic Modeling Of Atomic-Scale Friction, Yalin Dong
Physically Representative Atomistic Modeling Of Atomic-Scale Friction, Yalin Dong
Dr. Yalin Dong
Nanotribology is a research field to study friction, adhesion, wear and lubrication occurred between two sliding interfaces at nano scale. This study is motivated by the demanding need of miniaturization mechanical components in Micro Electro Mechanical Systems (MEMS), improvement of durability in magnetic storage system, and other industrial applications. Overcoming tribological failure and finding ways to control friction at small scale have become keys to commercialize MEMS with sliding components as well as to stimulate the technological innovation associated with the development of MEMS. In addition to the industrial applications, such research is also scientifically fascinating because it opens a …
Speed Dependence Of Atomic Stick-Slip Friction In Optimally Matched Experiments And Molecular Dynamics Simulations, Qunyang Li, Yalin Dong, Danny Perez, Ashlie Martini, Robert W. Carpick
Speed Dependence Of Atomic Stick-Slip Friction In Optimally Matched Experiments And Molecular Dynamics Simulations, Qunyang Li, Yalin Dong, Danny Perez, Ashlie Martini, Robert W. Carpick
Dr. Yalin Dong
The atomic stick-slip behavior of a Pt tip sliding on a Au(111) surface is studied with atomic force microscopy (AFM) experiments and accelerated (i.e., reduced sliding speed) molecular dynamics (MD) simulations. The MD and AFM conditions are controlled to match, as closely as possible, the geometry and orientation, load, temperature, and compliance. We observe clear stick-slip without any damage. Comparison of bothMDand AFM results with the thermally activated Prandtl-Tomlinson model shows that MD results at the highest speeds are not in the thermally activated regime. At lower speeds, within the thermally activated regime, AFM and MD provide consistent energetics, but …
Atomistic Study Of Lateral Contact Stiffness In Friction Force Microscopy, Huang Gao, Yalin Dong, Ashlie Martini
Atomistic Study Of Lateral Contact Stiffness In Friction Force Microscopy, Huang Gao, Yalin Dong, Ashlie Martini
Dr. Yalin Dong
The effective stiffness of a friction force microscope tip–substrate system is an important parameter that describes the relationship between lateral force and elastic deformation. In this study, we use a multi-spring model to simplify the system, where two contributions, the tip apex stiffness and the lateral contact stiffness, are discussed in detail. Molecular dynamics simulations are used to characterize stiffness by simulating a tip apex subject to shear or sliding over a substrate surface. The results show that, although the height of the tip apex and tip–substrate orientation affect the various stiffness contributions, the contact itself dominates the overall compliance.