Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Molecular modeling of crosslinked epoxy polymers: The effect of crosslink density on thermomechanical properties

This article reviews the field of molecular simula- tions of thermoset polymers. This class of polymers is of inter- est in applications ranging from structural components for aerospace to electronics packaging and predictive simulations of their response is playing an increasing role in understanding the molecular origin of their properties and complementing experiments in the search for tailored materials for specific applications. It focuses on modeling and simulation of the pro- cess of curing to predict the molecular structure of these poly- mers and their thermomechanical response by all-atom molecular dynamics simulations. Results from Monte Carlo and coarse-grained simulations are briefly summarized. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 00, 000-000

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/polb.23489

Molecular scale simulations on thermoset polymers: A review

The high performance multi-walled carbon nanotubes (MWNTs) reinforced epoxy polymer nanocomposites (PNCs) have been synthesized at different MWNT loading levels. The surface functionalization of MWNTs with conductive PANI was achieved by using a facile surface initiated polymerization method with the aid of the oxidations of CNTs and subsequent anilines by hexavalent chromium (Cr(VI)) oxidant. The effects of MWNT loading, surface functionalization and temperature on the rheological behaviors of liquid epoxy resin nanosuspensions and on the physicochemical properties of cured solid PNCs were systematically investigated. The glass transition temperature (Tg) of the cured epoxy PNCs filled with functionalized MWNTs obtained from the dynamic mechanical analysis (DMA) test was increased about 6–25 °C than that of cured pure epoxy. The PNCs reinforced with functionalized MWNTs demonstrated an enhanced tensile strength than either cured pure epoxy or its PNCs filled with the as-received MWNTs. The electrical conductivity of cured epoxy PNCs with functionalized MWNTs was improved by 5.5 orders of magnitude compared with cured pure epoxy. Thermogravimetric analysis (TGA) revealed an enhanced thermo-stability in the cured epoxy PNCs filled with functionalized MWNTs than that of cured pure epoxy and its PNCs filled with the as-received MWNTs. The observed strong interfacial interaction between MWNTs and the epoxy resin matrix was responsible for the enhanced mechanical tensile strength. The nanocomposite formation mechanism is proposed based on the analysis from Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), Raman and differential scanning calorimetry (DSC) tests.

Epoxy resin nanosuspensions and reinforced nanocomposites from polyaniline stabilized multi-walled carbon nanotubes

Recently, great attention has been focused on using epoxy polymers in different fields such as aerospace, automotive, biotechnology, and electronics, owing to their superior properties. In this study, the classical molecular dynamics (MD) was used to simulate the cross linking of diglycidyl ether of bisphenol-A (DGEBA) with diethylenetriamine (DETA) curing agent, and to study the behavior of resulted epoxy polymer with different conversion rates. The constant-strain (static) approach was then applied to calculate the mechanical properties (Bulk, shear and Young's moduli, elastic stiffness constants, and Poisson's ratio) of the uncured and cross-linked systems. Estimated material properties were found to be in good agreement with experimental observations. Moreover, the dependency of mechanical properties on the cross linking density was investigated and revealed improvements in the mechanical properties with increasing the cross linking density. The radial distribution function (RDF) was also used to study the evolution of local structures of the simulated systems as a function of cross linking density.

The effect of cross linking density on the mechanical properties and structure of the epoxy polymers: molecular dynamics simulation

https://ntrs.nasa.gov/api/citations/20090023547/downloads/20090023547.pdf

Molecular modeling for calculation of mechanical properties of epoxies with moisture ingress

The effective elastic properties of a unidirectional carbon fiber/epoxy lamina in which the carbon fibers are coated with single-walled carbon nanotubes are modeled herein through the use of a multi-scale method involving the molecular dynamics/equivalent continuum and micromechanics methods. The specific lamina representative volume element studied consists of a carbon fiber surrounded by a region of epoxy containing a radially varying concentration of carbon nanotubes which is then embedded in the pure epoxy matrix. The variable concentration of carbon nanotubes surrounding the carbon fiber results in a functionally graded interphase region as the properties of the interphase region vary according to the carbon nanotube volume fraction. Molecular dynamics and equivalent continuum methods are used to assess the local effective properties of the carbon nanotube/epoxy comprising the interphase region. Micromechanics in the form of the Mori-Tanaka method are then applied to obtain the global effective properties of the graded interphase region wherein the carbon nanotubes are randomly oriented. Finally, the multi-layer composite cylinders micromechanics approach is used to obtain the effective lamina properties from the lamina representative volume element. It was found that even very small quantities of carbon nanotubes (0.36% of lamina by volume) coating the surface of the carbon fibers in the lamina can have a significant effect (8% increase) on the transverse properties of the lamina (E22, k23, G23 and G12) with almost no affect on the lamina properties in the fiber direction (E11 and v12).

https://ntrs.nasa.gov/api/citations/20060014005/downloads/20060014005.pdf

Sarah Jane V. Frankland

Papers

Molecular modeling for calculation of mechanical properties of epoxies with moisture ingress

Micromechanics Modeling of Functionally Graded Interphase Regions in Carbon Nanotube-Polymer Composites

(Student Paper) Micromechanics Modeling of Functionally Graded Interphase Regions in Carbon Nanotube-Polymer Composites