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

Magnesium matrix nanocomposites reinforced with graphene nanoplatelets (GNPs) additives have long been considered as exciting prospects among nanotechnology applications. Here, the thixomolding process, an extremely efficient dispersing technology, was applied to prepare AZ91D magnesium alloy- GNPs nanocomposites with different GNPs contents (0, 0.1, 0.3, 0.6, 0.9 and 1.2 wt%). The effects of screw rotate rate (RS) and injection velocity (VI) on microstructures, GNPs dispersibility and mechanical properties were investigated. The GNPs, fairly uniform dispersion in the nanocomposites, were incorporated in the α-Mg grains, not only in the grain boundaries. Strong bonding interfaces between GNPs and alloy matrix were established because of the formed MgO nanoparticles leading to the formation of Mg/MgO semi-coherency interface and MgO/GNPs interface. Compared with other previously reported results, a relatively higher overall efficiency was achieved in the prepared magnesium matrix nanocomposites. The developed technology has a potential for large-scale industrial production of not only thin-walled complex parts, but also thick-walled products such as automobile parts with complex structure.

Reinforced AZ91D magnesium alloy with thixomolding process facilitated dispersion of graphene nanoplatelets and enhanced interfacial interactions

Interfaces in heterostructures of crystalline materials could strongly affect the slip of dislocations. Such interfaces have become one of the most popular methods to tailor material strength and ductility. This review focuses on the interaction of dislocations and interfaces in heterostructures, in which at least one component is metallic, as investigated by molecular dynamics, in order to systematically summarize our understanding about how dislocations interact with the interfaces. All the possible heterostructures of metallic materials are covered, such as twin boundaries, grain boundaries, bi-metal interfaces and metal/non-metal interfaces. Dislocations may either penetrate the interfaces by inducing steps into the interfaces or dissociate within the interfaces, depending on the type and orientation of the interface as well as the applied strain. Related dislocation interactions at the interface are also presented. In addition, we also discuss the effect of dislocation types, of applied strain and of the deformation method on the interaction of dislocations and interfaces.

https://www.mdpi.com/2073-4352/9/11/584/pdf

Interaction of Dislocations and Interfaces in Crystalline Heterostructures: A Review of Atomistic Studies

Self-energy, line tension and bow-out of grain boundary dislocation sources

Relaxation of dislocation structures under ultrasonic influence

Low-angle grain boundaries (LAGBs) may show up frequently as distinct dislocation products such as in the processes of work hardening, recovery and recrystallisation of metals and alloys. To reveal...

Yun Gao

Papers

Interaction between lattice dislocations and low-angle grain boundaries in Ni via molecular dynamics simulations