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

In recent years, Additive Manufacturing (AM), also called 3D printing, has been expanding into several industrial sectors due to the technology providing opportunities in terms of improved functionality, productivity, and competitiveness. While metal AM technologies have almost unlimited potential, and the range of applications has increased in recent years, industries have faced challenges in the adoption of these technologies and coping with a turbulent market. Despite the extensive work that has been completed on the properties of metal AM materials, there is still a need of a robust understanding of processes, challenges, application-specific needs, and considerations associated with these technologies. Therefore, the goal of this study is to present a comprehensive review of the most common metal AM technologies, an exploration of metal AM advancements, and industrial applications for the different AM technologies across various industry sectors. This study also outlines current limitations and challenges, which prevent industries to fully benefit from the metal AM opportunities, including production volume, standards compliance, post processing, product quality, maintenance, and materials range. Overall, this paper provides a survey as the benchmark for future industrial applications and research and development projects, in order to assist industries in selecting a suitable AM technology for their application.

Advances in Metal Additive Manufacturing: A Review of Common Processes, Industrial Applications, and Current Challenges

The ability to map plastic deformation around high strain gradient microstructural features is central in studying phenomena such as fatigue and stress corrosion cracking. A method for the visualization of plastic deformation in electron back-scattered diffraction (EBSD) data has been developed and is described in this article. This technique is based on mapping the intragrain misorientation in polycrystalline metals. The algorithm maps the scalar misorientation between a local minimum misorientation reference pixel and every other pixel within an individual grain. A map around the corner of a Vickers indentation in 304 stainless steel was used as a test case. Several algorithms for EBSD mapping were then applied to the deformation distributions around air fatigue and stress corrosion cracks in 304 stainless steel. Using this technique, clear visualization of a deformation zone around high strain gradient microstructural features (crack tips, indentations, etc.) is possible with standard EBSD data.

Misorientation mapping for visualization of plastic deformation via electron back-scattered diffraction.

The application of additively manufactured (AM) stainless steel (SS) parts is rapidly emerging in a broad spectrum of industries. Laser powder bed fusion (LPBF) and direct laser deposition (DLD) are the main AM methods to fabricate a vast range of SSs like 316 L, AISI 420, 17-4 PH, 304 L, and AISI 4135. This article focuses on the corrosion performance of additively manufactured stainless steel parts made by LPBF and DLD. The passive film formation mechanisms and the corrosion performance of LPBF/DLD AM SS parts are discussed in comparison to their conventionally made counterparts. Microstructural features like porosity, inclusions, residual stress, surface roughness, elemental segregation, phases, and grain size distribution are elaborated thoroughly from the corrosion point of view, closely linked with the AM processing parameters. Generally, process parameters play an important role in the corrosion properties of AM parts by impacting the microstructural features. Assuming a proper set of parameters for the printing process, the overall corrosion performance of AM SS is better than its conventional counterparts. However, there are still controversies around some important aspects such as passive film structure, the nature of residual stress, post heat treatment processes, and grain size distribution and their impact on corrosion performance, which emphasizes the need for future studies in this area.

Corrosion performance of additively manufactured stainless steel parts: A review

Customized manufacturing of a miniaturized device with micro and mesoscale features is a key requirement of mechanical, electrical, electronic and medical devices. Powder-based 3D-printing processes offer a strong candidate for micromanufacturing due to the wide range of materials, fast production and high accuracy. This study presents a comprehensive review of the powder-based three-dimensional (3D)-printing processes and how these processes impact the creation of devices with micro and mesoscale features. This review also focuses on applications of devices with micro and mesoscale size features that are created by powder-based 3D-printing technology.

Powder-Based 3D Printing for the Fabrication of Device with Micro and Mesoscale Features.

Study on direct laser metal deposition

Notch fatigue performance of DP600 steel under different pre-straining paths

Influence of uniaxial and biaxial pre-straining on the high cycle fatigue performance of DP590 steel

Monotonic and cyclic plastic deformation behavior of nanocrystalline gold was investigated at room temperature using molecular dynamics simulation. Yielding starts in nanocrystalline gold by initiation of 1/6 〈1 1 2〉 Shockley partial dislocation from the grain boundary. A stacking fault is created between the grain boundary and moved Shockley partial dislocation. With the progression of further deformation, increase in dislocation density inside the grain, the formation of dislocation locks such as Stair-rod 1/6 〈1 1 0〉 and Hirth 1/3 〈1 0 0〉 dislocations, generation and removal of stacking fault tetrahedron are observed. Grain coarsening and a rise in the number of dislocation inside the grains were noted with an increasing number of cycles.

Puja Ghosal

Papers

Study on direct laser metal deposition

Notch fatigue performance of DP600 steel under different pre-straining paths

Influence of uniaxial and biaxial pre-straining on the high cycle fatigue performance of DP590 steel

Monotonic and cyclic plastic deformation behavior of nanocrystalline gold: atomistic simulations

Influence of uniaxial and biaxial pre-straining on the notch fatigue performance of DP590 steel