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

https://dc.engconfintl.org/cgi/viewcontent.cgi?article=1032&context=superalloys_ii

A critical review of high entropy alloys and related concepts

Microstructures and properties of high-entropy alloys

High-entropy alloys (HEAs) are alloys with five or more principal elements. Due to the distinct design concept, these alloys often exhibit unusual properties. Thus, there has been significant interest in these materials, leading to an emerging yet exciting new field. This paper briefly reviews some critical aspects of HEAs, including core effects, phases and crystal structures, mechanical properties, high-temperature properties, structural stabilities, and corrosion behaviors. Current challenges and important future directions are also pointed out.

https://www.tandfonline.com/doi/pdf/10.1080/21663831.2014.912690

High-Entropy Alloys: A Critical Review

Overview of constitutive laws, kinematics, homogenization and multiscale methods in crystal plasticity finite-element modeling: Theory, experiments, applications

When a crystal deforms plastically, phenomena such as dislocation storage, multiplication, motion, pinning, and nucleation occur over the submicron-to-nanometer scale. Here we report measurements of plastic yielding for single crystals of micrometer-sized dimensions for three different types of metals. We find that within the tests, the overall sample dimensions artificially limit the length scales available for plastic processes. The results show dramatic size effects at surprisingly large sample dimensions. These results emphasize that at the micrometer scale, one must define both the external geometry and internal structure to characterize the strength of a material.

http://science.sciencemag.org/content/sci/305/5686/986.full.pdf

Sample dimensions influence strength and crystal plasticity.

This review examines the recent literature that has focused on uniaxial compression experiments of single crystals at the micrometer scale. Collectively, the studies discovered new regimes of plastic flow that are size-scale dependent and that occur in the absence of strong strain gradients. However, the quantitative comparison of the flow curves between independent studies is hampered by differences in the particular implementations of the testing methodology. Modeling of microcompression experiments using 3-D discrete dislocation simulations has provided valuable insight into the mechanisms that control plastic flow in FCC metals. These efforts identified the importance of the initial dislocation density and distribution of mobile dislocation segments, the influence of free surfaces on that distribution, as well as altered multiplication and hardening responses due to the finite source statistics. Microcrystal experiments also provide a new pathway to characterize the global system dynamics of dislocati...

Plasticity of Micrometer-Scale Single Crystals in Compression

Size-affected single-slip behavior of pure nickel microcrystals

During the last two years remarkable improvements have been made in the properties (such as toughness and creep) and processing technology of gamma titanium aluminides, making them potentially viable engineering alloys for high-temperature structural applications. These achievements were made possible by a greater understanding of both the fundamental and the practical aspects of these aluminides, such as phase relationships, the effects of alloying elements, deformation mechanisms, microstructure evolution and processing. This article reviews the current understanding of the above specific aspects and the processing-microstructure-property relationships, and identifies pacing problems and applications.

Dennis M. Dimiduk

Papers

Sample dimensions influence strength and crystal plasticity.

Plasticity of Micrometer-Scale Single Crystals in Compression

Size-affected single-slip behavior of pure nickel microcrystals

Progress in the understanding of gamma titanium aluminides

Contribution to size effect of yield strength from the stochastics of dislocation source lengths in finite samples