Contact and Friction at Nanoscale

2008 ◽  
Vol 33-37 ◽  
pp. 999-1004 ◽  
Author(s):  
X.M. Liu ◽  
X. You ◽  
Zhuo Zhuang
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Microstructure Evolution ◽  
Md Simulations ◽  
Dislocation Nucleation ◽  
Dislocation Loops ◽  
Friction Energy ◽  
Energy Dissipated ◽  
Disordered Atoms

Molecular Dynamics (MD) simulations of indentation and scratch over crystal nickel (100) were carried out to investigate the microstructure evolution at nanoscale. The dislocation nucleation and propagation during process were observed preferably between close-packed planes. Dislocation loops are formed under both indentation and scratch process, and indentation and friction energy were transferred to the substrate in the form of phonon of disordered atoms, then part of the energy dissipated and rest is remain in the form of permanent plastic deformation.

Microstructure evolution and plastic deformation of Ni47Co53 alloy under tension

CrystEngComm ◽  
2022 ◽  
Author(s):  
ruibo ma ◽  
Lili Zhou ◽  
Yong-Chao Liang ◽  
Ze-an Tian ◽  
Yun-Fei Mo ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Rapid Solidification ◽  
Microstructural Evolution ◽  
Microstructure Evolution ◽  
Cooling Rates ◽  
Solidification Processes ◽  
Molecular Dynamics Methods

To investigate microstructural evolution and plastic deformation under tension conditions, the rapid solidification processes of Ni47Co53 alloy are first simulated by molecular dynamics methods at cooling rates of 1011, 1012...

The Challenges of Sliding Wear

2005 ◽  
Author(s):  
D. A. Rigney
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Wear Debris ◽  
Sliding Wear ◽  
Md Simulations ◽  
Mechanical Mixing ◽  
Wear Model ◽  
Two Fluids ◽  
Continuum Analysis

The production of nanocrystalline wear debris containing components from the worn specimen, from the counterface and from the environment does not support any of the better known wear models or wear equations based on adhesion, delamination, fatigue or oxidation. In this presentation, plastic deformation, mechanical mixing and patterns of flow determined from experiments will be compared with molecular dynamics (MD) simulations and a continuum analysis of two ‘fluids’ shearing in opposite directions. Together, these suggest generic behavior that needs to be included in any realistic sliding wear model.

Cascades Damage in γ-Iron from Molecular Dynamics Simulations

2020 ◽  
Vol 993 ◽  
pp. 1011-1016
Author(s):  
Shi Wu ◽  
Han Cao ◽  
Dong Jie Wang ◽  
Li Xia Jia ◽  
Yan Kun Dou
Keyword(s):  
Molecular Dynamics ◽  
Austenitic Stainless Steels ◽  
Md Simulations ◽  
Atomic Displacement ◽  
Dislocation Loops ◽  
Vacancy Clusters ◽  
Displacement Cascade ◽  
Dynamics Simulations ◽  
Peak Value ◽  
Stable Stage

The degradation of austenitic stainless steels under irradiation environment is a known problem for nuclear reactors, which starts from atoms displacement cascade. Here, molecular dynamics (MD) simulations have been used to investigate the formation of atomic displacement cascade in γ-iron for energies of the primary knock-on atom (PKA) up to 40 keV at 300 K. The number of Frenkel pairs increased sharply until a peak value was reached, which occurred at a time in the range of 0.1-2 ps. After that, a number of defects gradually decreased and became stabilized. Compared with α-iron, there was less defects in the stable stage, and more clustered defects were produced in γ-iron. Within the range of PKA energies, two regimes of power-law energy-dependence of the defect production were observed, which converge on 16.8 keV. The transition energy also marks the onset of the formation of large self-interstitial atom (SIA) clusters and vacancy clusters. Interstitial and vacancy clusters were in the form of Shockley, Frank dislocation loops and Stir-Rod dislocation loops.

An investigation of nanoindentation tests on the single crystal copper thin film via an atomic force microscope and molecular dynamics simulation

2007 ◽  
Vol 221 (2) ◽  
pp. 259-266 ◽  
Author(s):  
D Huo ◽  
Y Liang ◽  
K Cheng
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Size Effect ◽  
Single Crystal ◽  
Atomic Force Microscope ◽  
Md Simulations ◽  
Single Crystal Copper ◽  
Atomic Force

Nanoindentation tests performed in an atomic force microscope have been utilized to directly measure the mechanical properties of single crystal metal thin films fabricated by the vacuum vapour deposition technique. Nanoindentation tests were conducted at various indentation depths to study the effect of indentation depths on the mechanical properties of thin films. The results were interpreted by using the Oliver-Pharr method with which direct observation and measurement of the contact area are not required. The elastic modulus of the single crystal copper film at various indentation depths was determined as 67.0 > 6.9 GPa on average, which is in reasonable agreement with the results reported by others. The indentation hardness constantly increases with decreasing indentation depth, indicating a strong size effect. In addition to the experimental work, a three-dimensional nanoindentation model of molecular dynamics (MD) simulations with embedded atom method (EAM) potential is proposed to elucidate the mechanics and mechanisms of nanoindentation of thin films from the atomistic point of view. MD simulations results show that due to the size effect no distinct dislocations were observed in the plastic deformation processes of the single crystal copper thin films, which is significantly different from the plastic deformation mechanism in bulk materials.

Nanoindentation-Induced Collective Dislocation Behavior and Nanoplasticity

2007 ◽  
Vol 340-341 ◽  
pp. 39-48 ◽  
Author(s):  
Yoji Shibutani ◽  
Tomohito Tsuru
Keyword(s):  
Three Dimensional ◽  
Md Simulations ◽  
Dislocation Nucleation ◽  
Balance Model ◽  
Shear Stresses ◽  
Dislocation Loops ◽  
Nucleation Model ◽  
Dislocation Behavior ◽  
Discrete Dislocations ◽  
The Ideal

The present paper summarizes the crystallographic dependence of the displacement burst behavior observed in nanoindentation using two single crystalline aluminum (Al) materials and copper (Cu) with three kinds of surface indices, namely (001), (110) and (111). From the critical indent load at the first burst, the critical resolved shear stresses (CRSSs) of the collective dislocation nucleation were estimated in reference to molecular dynamics (MD) simulations. These are almost one-tenth of the shear modulus, which are close to the ideal values. We explain the nanoplastic mechanics by a comprehensive energy balance model to describe the linear relation between the indent load and the burst width of the first displacement burst and by the nucleation model consisting of three-dimensional discrete dislocations to evaluate the number of dislocations nucleating. The distance between the emitted dislocation loops of Al is found to be fairly large. Thus, Al is expected to exhibit a less tangled network of dislocations just below the indentation than Cu, which has a lower stacking fault energy.

Effect of Initial Indentation Position on Plastic Deformation Behaviors of Polycrystalline Materials via Molecular Dynamics Simulation

NANO ◽  
2019 ◽  
Vol 14 (01) ◽  
pp. 1950001 ◽  
Author(s):  
Pengyue Zhao ◽  
Yongbo Guo
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Potential Energy ◽  
Internal Stress ◽  
Position Effect ◽  
Md Simulations ◽  
Dynamics Simulation ◽  
Polycrystalline Materials ◽  
Indentation Force ◽  
Deformation Behaviors

Polycrystalline materials can be divided into four types of microstructural components, including grain cell (GC), grain boundary (GB), triple junction (TJ) and vertex points (VP). Nanoindentation at different microstructural components on the polycrystalline materials surface can lead to different plastic deformation behaviors of the polycrystalline materials. Due to experimental limitations, the indentation-induced internal stress and defect evolution process are difficult to investigate directly, especially for the polycrystalline materials with grain size less than 100[Formula: see text]nm. The molecular dynamics (MD) simulations were performed to unravel the initial indentation position effect on the elasticity/plastic deformation mechanism of polycrystalline copper. The results reveal that the initial indentation position governs the indentation force variation and defect distribution range due to the different dimensionalities of the microstructural components. The defect propagation as well as the internal stress transmission in the GC regions tend to transfer to the low-dimensional microstructural components of the interfaces. In addition, the atomic internal stress and potential energy accumulation/release of the microstructural component atoms during the nanoindentation process are also investigated, revealing that the atomic internal stress and potential energy in the VPs vary earliest, followed by the TJs, GBs and GCs.

scholarly journals High-Rate Plastic Deformation of Nanocrystalline Tantalum to Large Strains: Molecular Dynamics Simulation

2009 ◽  
Vol 633-634 ◽  
pp. 3-19 ◽  
Author(s):  
Robert E. Rudd
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Large Scale ◽  
Amorphous Solid ◽  
Md Simulations ◽  
High Rate ◽  
Dynamics Simulation ◽  
Biaxial Compression ◽  
Large Strains ◽  
Fine Grained

Recent advances in the ability to generate extremes of pressure and temperature in dynamic experiments and to probe the response of materials has motivated the need for special materials optimized for those conditions as well as a need for a much deeper understanding of the behavior of materials subjected to high pressure and/or temperature. Of particular importance is the understanding of rate effects at the extremely high rates encountered in those experiments, especially with the next generation of laser drives such as at the National Ignition Facility. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum to investigate the processes associated with plastic deformation for strains up to 100%. We use initial atomic configurations that were produced through simulations of solidification in the work of Streitz et al [Phys. Rev. Lett. 96, (2006) 225701]. These 3D polycrystalline systems have typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. This analysis technique is robust and fast, and has been used to compute the orientations on the fly during our parallel MD simulations on supercomputers. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures.

Efficient Treatment of Fixed and Induced Dipolar Interactions

2000 ◽  
Vol 653 ◽  
Author(s):  
Celeste Sagui ◽  
Thoma Darden
Keyword(s):  
Molecular Dynamics ◽  
Md Simulations ◽  
Lagrangian Formalism ◽  
Dipolar Interactions ◽  
Time Step ◽  
Efficient Treatment ◽  
Particle Mesh Ewald ◽  
Fixed Charges ◽  
Self Consistency ◽  
Induced Dipoles

AbstractFixed and induced point dipoles have been implemented in the Ewald and Particle-Mesh Ewald (PME) formalisms. During molecular dynamics (MD) the induced dipoles can be propagated along with the atomic positions either by interation to self-consistency at each time step, or by a Car-Parrinello (CP) technique using an extended Lagrangian formalism. The use of PME for electrostatics of fixed charges and induced dipoles together with a CP treatment of dipole propagation in MD simulations leads to a cost overhead of only 33% above that of MD simulations using standard PME with fixed charges, allowing the study of polarizability in largemacromolecular systems.

Split the Charge Difference in Two! a Rule of Thumb for Adding Proper Amounts of Ions in MD Simulations

2020 ◽  
Author(s):  
Matías R. Machado ◽  
Sergio Pantano
Keyword(s):  
Molecular Dynamics ◽  
Ionic Strength ◽  
Molecular Simulations ◽  
Md Simulations ◽  
Good Practices ◽  
Rule Of Thumb ◽  
Ionic Concentrations

<p> Despite the relevance of properly setting ionic concentrations in Molecular Dynamics (MD) simulations, methods or practical rules to set ionic strength are scarce and rarely documented. Based on a recently proposed thermodynamics method we provide an accurate rule of thumb to define the electrolytic content in simulation boxes. Extending the use of good practices in setting up MD systems is promptly needed to ensure reproducibility and consistency in molecular simulations.</p>

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