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Molecular dynamics simulation of dynamic response of beryllium

AIP Conference Proceedings

Thompson, Aidan P.; Lane, James M.; Desjarlais, Michael P.

The response of beryllium to dynamic loading has been extensively studied, both experimentally and theoretically, due to its importance in several technological areas. We use a MEAM empirical potential to examine the melt transition. MD simulations of equilibrated two-phase systems were used to calculate the HCP melting curve up to 300 GPa. This was found to agree well with previous ab initio calculations. The Hugoniostat method was used to examine dynamic compression along the two principal orientations of the HCP crystal. In both directions, the melting transition occurred at 230 GPa and 5000 K, consistent with the equilibrium melting curve. Direct NEMD simulations of uniaxial compression show a transition to an amorphous material at shocked states that lie below the equilibrium melt curve. © 2012 American Institute of Physics.

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TYPE Journal Article YEAR 2012
OSTIScopus

Molecular dynamics simulation of shock-compressed hydrocarbon polymers and foams

ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials

Lane, James M.; Grest, Gary S.; Mattsson, Thomas M.

Hydrocarbon polymers, foams and nanocomposites are increasingly being subjected to extreme environments. Molecular scale modeling of these materials offers insight into failure mechanisms and complex response. Classical molecular dynamics (MD) simulations of the principal shock Hugoniot were conducted for two hydrocarbon polymers, polyethylene (PE) and poly(4-methyl-1-pentene) (PMP). We compare these results with recent density functional theory (DFT) calculations and experiments conducted at Sandia National Laboratories. Here, we extend these results to include low-density polymer foams using nonequilibrium MD techniques. We find good quantitative agreement with experiment. Further, we have measured local temperatures to investigate the formation of hot spots and polymer dissociation near foam voids.

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TYPE Conference YEAR 2012
OSTIScopus

Modeling ramp compression experiments using large-scale molecular dynamics simulation

Thompson, Aidan P.; Lane, James M.; Zimmerman, Jonathan A.

Molecular dynamics simulation (MD) is an invaluable tool for studying problems sensitive to atomscale physics such as structural transitions, discontinuous interfaces, non-equilibrium dynamics, and elastic-plastic deformation. In order to apply this method to modeling of ramp-compression experiments, several challenges must be overcome: accuracy of interatomic potentials, length- and time-scales, and extraction of continuum quantities. We have completed a 3 year LDRD project with the goal of developing molecular dynamics simulation capabilities for modeling the response of materials to ramp compression. The techniques we have developed fall in to three categories (i) molecular dynamics methods (ii) interatomic potentials (iii) calculation of continuum variables. Highlights include the development of an accurate interatomic potential describing shock-melting of Beryllium, a scaling technique for modeling slow ramp compression experiments using fast ramp MD simulations, and a technique for extracting plastic strain from MD simulations. All of these methods have been implemented in Sandia's LAMMPS MD code, ensuring their widespread availability to dynamic materials research at Sandia and elsewhere.

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TYPE SAND Report YEAR 2011
DOIOSTI

Molecular dynamics simulations of water confined between matched pairs of hydrophobic and hydrophilic self-assembled monolayers

Proposed for publication in Langmuir.

Stevens, Mark J.; Lane, James M.; Grest, Gary S.; Chandross, M.

We have conducted a molecular dynamics (MD) simulation study of water confined between methyl-terminated and carboxyl-terminated alkylsilane self-assembled monolayers (SAMs) on amorphous silica substrates. In doing so, we have investigated the dynamic and structural behavior of the water molecules when compressed to loads ranging from 20 to 950 MPa for two different amounts of water (27 and 58 water molecules/nm{sup 2}). Within the studied range of loads, we observe that no water molecules penetrate the hydrophobic region of the carboxyl-terminated SAMs. However, we observe that at loads larger than 150 MPa water molecules penetrate the methyl-terminated SAMs and form hydrogen-bonded chains that connect to the bulk water. The diffusion coefficient of the water molecules decreases as the water film becomes thinner and pressure increases. When compared to bulk diffusion coefficients of water molecules at the various loads, we found that the diffusion coefficients for the systems with 27 water molecules/nm{sup 2} are reduced by a factor of 20 at low loads and by a factor of 40 at high loads, while the diffusion coefficients for the systems with 58 water molecules/nm{sup 2} are reduced by a factor of 25 at all loads.

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TYPE Journal Article YEAR 2008
OSTI
Results 101–120 of 120
Results 101–120 of 120