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

Additive manufacturing enables the printing of metallic parts, such as customized implants for patients, durable single-crystal parts for use in harsh environments, and the printing of parts with site-specific chemical compositions and properties from 3D designs. However, the selection of alloys, printing processes and process variables results in an exceptional diversity of microstructures, properties and defects that affect the serviceability of the printed parts. Control of these attributes using the rich knowledge base of metallurgy remains a challenge because of the complexity of the printing process. Transforming 3D designs created in the virtual world into high-quality products in the physical world needs a new methodology not commonly used in traditional manufacturing. Rapidly developing powerful digital tools such as mechanistic models and machine learning, when combined with the knowledge base of metallurgy, have the potential to shape the future of metal printing. Starting from product design to process planning and process monitoring and control, these tools can help improve microstructure and properties, mitigate defects, automate part inspection and accelerate part qualification. Here, we examine advances in metal printing focusing on metallurgy, as well as the use of mechanistic models and machine learning and the role they play in the expansion of the additive manufacturing of metals. Several key industries routinely use metal printing to make complex parts that are difficult to produce by conventional manufacturing. Here, we show that a synergistic combination of metallurgy, mechanistic models and machine learning is driving the continued growth of metal printing.

Metallurgy, mechanistic models and machine learning in metal printing

Metal additive manufacturing technologies, such as powder bed fusion process, directed energy deposition (DED) process, sheet lamination process, etc., are one of promising flexible manufacturing technologies due to direct fabrication characteristics of a metallic freeform with a three-dimensional shape from computer aided design data. DED processes can create an arbitrary shape on even and uneven substrates through line-by-line deposition of a metallic material. Theses DED processes can easily fabricate a heterogeneous material with desired properties and characteristics via successive and simultaneous depositions of different materials. In addition, a hybrid process combining DED with different manufacturing processes can be conveniently developed. Hence, researches on the DED processes have been steadily increased in recent years. This paper reviewed recent research trends of DED processes and their applications. Principles, key technologies and the state-of-the art related to the development of process and system, the optimization of deposition conditions and the application of DED process were discussed. Finally, future research issues and opportunities of the DED process were identified.

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Directed Energy Deposition (DED) Process: State of the Art

Today, developments in technology have gained momentum more than ever, and the need for efficiency in production as well as in the ecological domain has increased significantly. Studies examining dry machining and coolant removal have been superseded by those presenting new cooling and lubrication techniques. The effects on surface roughness directly related to final product quality are being investigated in terms of tool life and employee health. This has resulted in more frequent use of the eco-friendly minimum quantity lubrication (MQL) technique, which has now become a major competitor to dry and coolant machining. In this study, AISI D2 cold work tool steel, a material widely used in the mold industry, was used as the workpiece. Tests were carried out under dry and MQL conditions and the temperature, cutting tool vibration amplitude, tool wear, surface roughness and tool life were evaluated. The experiments were carried out using two different cutting tool coating types (CVD-chemical vapor deposition and PVD-physical vapor deposition) and three different cutting speeds (60, 90 and 120 m/min) at a constant cutting depth (1 mm) and feed rate (0.09 mm/rev). Results revealed that tool wear, cutting temperature and cutting tool vibration amplitude were lower by 23, 25, and 45%, respectively, compared to dry cutting. Because of these improvements, the surface roughness of the workpiece was improved by 89% and tool life was increased by up to 267%.

The effect of vibration and cutting zone temperature on surface roughness and tool wear in eco-friendly MQL turning of AISI D2

Additive manufacturing of low-cost porous titanium-based composites for biomedical applications: Advantages, challenges and opinion for future development

Both modal analysis procedure and the results obtained on a three-component 3D-printed carbon-fiber reinforced composite (CFRC) are presented. Experimental modal analysis of on the composite has been carried out to obtain the dynamic behavior characteristics. As revealed, the different eigen-oscillations waveforms possess different sensitivity of its amplitude frequency response to structural defects of the composite. For the similar waveforms we observed the differences in eigen-oscuillation frequencies, vibration velocities and damping factors which can be caused by the presence of numerous defects homogeneously distributed in one of the samples.

The Use of Laser-Doppler Vibrometry for Modal Analysis of Carbon-Fiber Reinforced Composite

Microtexturing the metal cutting tool surfaces is a novel technique intended for enhancing the workability of these tools. The microtexturing is used in machining the titanium alloys for air-space applications for reducing the adhesion wear of metal cutting blades. This paper is focused on forming the microtextured dotted, banded and overlapped areas on the surfaces of high-speed steel samples. The treated areas have been examined using laser scanning microscopy for the microtexture pattern and roughness. It has been shown that the microtextured surfaces obtained on the high-speed steel samples were free of cracks. Surface pattern and roughness of all three microtextured areas have been examined and analyzed.

Oriented microtexturing on the surface of high-speed steel cutting tool

The results of the tensile tests carried out both on AMg5 (5083) aluminum alloy samples base and those obtained using friction stir processing technique are reported. The tensile test samples have been prepared from the friction stir processed plates so that their tensile axis was parallel to the processing direction. The maximum tensile strength of the processed samples was 9% higher than of the base metal. The fractographic examination shows the presence of flat areas inherent of the brittle fracture in all three friction processed samples. The load-extension curves show that friction stir processing may suppress the serrated yielding.

Tensile strength on friction stir processed AMg5 (5083) aluminum alloy

The effect of equal-channel angle pressing (ECAP) conditions on wear resistance and adhesion of the resulted ultrafine grained AA6063 in sliding against a steel ball has been investigated. Using the 3D laser confocal microscopy the parameters of wear and adhesion transfer layer thickness on ultrafine grained AA6063 has been measured. As it was established, the ECAP at room temperature allowed forming AA6063 microstructure in sliding, which is more wear resistant and less prone to adhesion as compared to the previous one at higher temperatures. The effect of ECAP pass number n on the above parameters becomes negligible for n > 8. The wear resistance of AA6063 processed by ECAP at 200°C is improved only for n = 4 whereas n > 4 has only a negative effect.

Adhesion transfer layer formation in sliding on equal-channel angle pressed ultrafine grained AA6063

Multilayer nitride coatings provide some of the best performance when in their use for the production of metalworking tools. In this work, vacuum-arc plasma-assisted deposited multilayer ZrN/CrN coatings with different numbers of constituent layers were characterized for high-temperature oxidization in air using weighing, confocal and scanning electron microscopy and synchrotron XRD. Oxidizing at 300 °C did not deteriorate the coating surfaces, while higher temperatures caused surface deterioration and oxidation accompanied by cracking, delamination and considerable mass gains. The coating with higher number of thinner layers showed higher oxidation resistance due to more prominent oxygen barrier effect.

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Andrey V. Filippov

Papers

The Use of Laser-Doppler Vibrometry for Modal Analysis of Carbon-Fiber Reinforced Composite

Oriented microtexturing on the surface of high-speed steel cutting tool

Tensile strength on friction stir processed AMg5 (5083) aluminum alloy

Adhesion transfer layer formation in sliding on equal-channel angle pressed ultrafine grained AA6063

High-Temperature Oxidation of CrN/ZrN Multilayer Coatings