Shockwave-induced plasticity via large-scale nonequilibrium molecular dynamics

1998 ◽  
Author(s):  
Brad Lee Holian
Keyword(s):  
Molecular Dynamics ◽  
Large Scale ◽  
Nonequilibrium Molecular Dynamics

Large-scale elastic-plastic indentation simulations via nonequilibrium molecular dynamics

1990 ◽  
Vol 42 (10) ◽  
pp. 5844-5853 ◽  
Author(s):  
William G. Hoover ◽  
Anthony J. De Groot ◽  
Carol G. Hoover ◽  
Irving F. Stowers ◽  
Toshio Kawai ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Large Scale ◽  
Nonequilibrium Molecular Dynamics ◽  
Elastic Plastic ◽  
Plastic Indentation

scholarly journals Shear Rheology of Unentangled and Marginally Entangled Ring Polymer Melts from Large-Scale Nonequilibrium Molecular Dynamics Simulations

Polymers ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1194 ◽  
Author(s):  
Alexandros J. Tsamopoulos ◽  
Anna F. Katsarou ◽  
Dimitrios G. Tsalikis ◽  
Vlasis G. Mavrantzas
Keyword(s):  
Molecular Dynamics ◽  
Flow Field ◽  
Large Scale ◽  
Nonequilibrium Molecular Dynamics ◽  
Survival Times ◽  
Dynamic Heterogeneity ◽  
Shear Rheology ◽  
Time Dynamics ◽  
Shear Rates ◽  
Wide Range

We present results for the steady state shear rheology of non-concatenated, unentangled and marginally entangled ring poly(ethylene oxide) (PEO) melts from detailed, atomistic nonequilibrium molecular dynamics (NEMD) simulations, and compare them to the behavior of the corresponding linear melts. The applied flow field spans a wide range of shear rates, from the linear (Newtonian) to the highly non-linear (described by a power law) regime. For all melts studied, rings are found to exhibit shear thinning but to a lesser degree compared to linear counterparts, mostly due to their reduced deformability and stronger resistance to alignment in the direction of flow. These features are attributed to the more compact structure of ring molecules compared to linear chains; the latter are capable of adopting wider and more open conformations even under shear due to the freedom provided by the free ends. Similar to linear melts, rings also exhibit a first and a second normal stress coefficient; the latter is negative. The ratio of the magnitude of the two coefficients remains practically constant with shear rate and is systematically higher than the corresponding one for linear melts. Emphasis was also given to the statistics of terminal (re-orientational) relaxation times which we computed by analyzing all chains in the simulated systems one by one; it was demonstrated that long time dynamics are strongly heterogeneous both for rings and (especially) linears. Repeating the analysis under flow conditions, and as expected, we found that the applied flow field significantly suppresses dynamic heterogeneity, especially for high shear rates well beyond the Newtonian plateau. Finally, a detailed geometrical analysis revealed that the average population of ring–ring threading events in the longest melt studied here (the PEO-5k ring) remains practically unaffected by the imposed flow rate even at strong shear rates, except for multi-threadings which disappear. To further analyze this peculiar and rather unexpected effect, we computed the corresponding survival times and penetration lengths, and found that the overwhelming majority of threadings under shear are extremely weak constraints, as they are characterized by very small penetration lengths, thus also by short survival times. They are expected therefore to play only a minor (if any) role on chain dynamics.

scholarly journals EQUILIBRIUM MOLECULAR DYNAMICS CALCULATIONS OF THERMAL CONDUCTIVITY: A “HOW-TO” FOR THE BEGINNERS

2020 ◽  
Vol 9 (1) ◽  
pp. 11-25
Author(s):  
Jude S. Alexander ◽  
Christopher Maxwell ◽  
Jeremy Pencer ◽  
Mouna Saoudi
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Large Scale ◽  
Interatomic Potential ◽  
Negative Impact ◽  
Significant Risk ◽  
Nonequilibrium Molecular Dynamics ◽  
Atomistic Modelling ◽  
Dynamics Simulations

The ready availability of codes such as LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) for molecular dynamics simulations has opened up the realm of atomistic modelling to novice code users with an interest in computational materials modelling but who lack the appropriate theoretical or computational background. As such, there is significant risk of the “user effect” having a negative impact on the quality of results obtained using such codes. Here, we present a “how-to” procedure for equilibrium molecular dynamics-based nuclear fuel thermal conductivity calculations using the Green–Kubo method with an interatomic potential developed by Cooper et al. [ 1 ]. The various steps of the simulation are identified and explained, along with criteria to assess the quality of the intermediate and final results, discussion of some problems that can arise during a simulation, and some inherent limitations of the method. Calculated thermal conductivities for UO2 and ThO2 will be compared with the available experimental data and also with similar thermal conductivity calculations using nonequilibrium molecular dynamics, reported in the open literature.

Nanoscale Structure and High Velocity Sliding at Cu/Ag Interfaces

2004 ◽  
Vol 821 ◽  
Author(s):  
James E. Hammerberg ◽  
Timothy C. Germann ◽  
Brad Lee Holian ◽  
Ramon Ravelo
Keyword(s):  
Molecular Dynamics ◽  
Single Crystals ◽  
Large Scale ◽  
Tangential Force ◽  
Nonequilibrium Molecular Dynamics ◽  
Embedded Atom Method ◽  
Dry Sliding ◽  
Embedded Atom ◽  
Sec System ◽  
Nanoscale Structure

AbstractWe present the results of large-scale NonEquilibrium Molecular Dynamics (NEMD) simulations for Cu/Ag interfaces sliding in the velocity regime 0≤v≤1Km/sec. System sizes of 2.8 × 106 atoms are considered using Embedded Atom Method (EAM) potentials. Single crystals with 010 interfaces sliding along the <100> direction are considered. We discuss the observed velocity weakening in the tangential force at high velocities, and its connection with the observed dislocation structure and nanostructure that are nucleated during dry sliding.

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