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

Premises of creation of Internet portal designed to provide access to participants of educational and scientific process for the joint creation, consolidation, concentration and rapid spreading of educational and scientific information resources in its own depository are considered. CMS-based portal content management systems’ potentiality is investigated. Architecture for Internet portal of MES of Ukraine’s information resources is offered.

Створення порталу інформаційно-довідкових ресурсів міністерства освіти і науки україни

Characterization and Properties of Natural Fiber Polymer Composites: A Comprehensive Review

Rapid innovation in nanotechnology in recent years enabled development of advanced metal matrix nanocomposites for structural engineering and functional devices. Carbonous materials, such as graphite, carbon nanotubes (CNT's), and graphene possess unique electrical, mechanical, and thermal properties. Owe to their lubricious nature, these carbonous materials have attracted researchers to synthesize lightweight self-lubricating metal matrix nanocomposites with superior mechanical and tribological properties for several applications in automotive and aerospace industries. This review focuses on the recent development in mechanical and tribological behavior of self-lubricating metallic nanocomposites reinforced by carbonous nanomaterials such as CNT and graphene. The review includes development of self-lubricating nanocomposites, related issues in their processing, their characterization, and investigation of their tribological behavior. The results reveal that adding CNT and graphene to metals decreases both coefficient of friction and wear rate as well as increases the tensile strength. The mechanisms involved for the improved mechanical and tribological behavior is discussed.

Mechanical and tribological properties of self-lubricating metal matrix nanocomposites reinforced by carbon nanotubes (CNTs) and graphene – A review

Friction stir welding (FSW) is a widely used solid state joining process for soft materials such as aluminium alloys because it avoids many of the common problems of fusion welding. Commercial feasibility of the FSW process for harder alloys such as steels and titanium alloys awaits the development of cost effective and durable tools which lead to structurally sound welds consistently. Material selection and design profoundly affect the performance of tools, weld quality and cost. Here we review and critically examine several important aspects of FSW tools such as tool material selection, geometry and load bearing ability, mechanisms of tool degradation and process economics.

Review: friction stir welding tools

Friction can influence the quality of the finished product to a large extent in certain manufacturing processes. Sheet metal forming is a particular case, where the friction between the hard-die and the relatively soft work-piece can be extremely important. Under such conditions, topography of the harder surface can influence the resistance to traction at the interface. This paper discusses about the correlation between certain features of the surface; topography and coefficient of friction based on experiments involving sliding of a few soft metal pins against a harder material. A brief description of the experimental procedure and the analysis are presented. A hybrid parameter which encapsulates both the amplitude features as well as the relative packing of peaks is shown to correlate well with the coefficient of friction.

Correlating the Features of Topography to Friction by Sliding Experiments

Value addition to coconut - opportunities and challenges.

Optimization of friction stir welding parameters for precipitation hardenable aluminum alloys 7020 and 6061

Surface texture of a tool plays an important role as it primarily controls the frictional behavior at the tribo interface. In the present investigation, pin-on-plate sliding tester was used to identify the effect of directionality of surface grinding marks on coefficient of friction and transfer layer formation. 080 M40 steel plates were ground to achieve different surface roughness with unidirectional grinding marks. Super purity aluminium pins were slid at a sliding velocity of 2 mm/s against the prepared steel plates. Grinding angle (i.e., the angle between direction of sliding and grinding marks) was varied between 0 o and 90 o in the tests. Normal load was varied from 0 to 120 N during the tests. Experiments were conducted under both dry and lubricated conditions in ambient environment. Scanning electron micrographs of the contact surfaces of pins and plates were used to study the surface features that included the morphology of the transfer layer. Surface roughness parameters of the steel plates were measured in the direction of the sliding using an optical profilometer. It was observed that the coefficient of friction and transfer layer formation depends primarily on the directionality of the grinding marks of the harder mating surface. Under lubricated conditions, stick-slip phenomena was observed, the amplitude of which depends on the plowing component of friction. The presence of stick-slip motion under lubricated conditions could be attributed to the molecular deformation of the lubricant component confined between asperities. The grinding angle effect on coefficient of friction was attributed to the variation in plowing component of friction, which in turn depends on the mean slope of the profile of the harder mating surface.

Satish V. Kailas

Papers

Correlating the Features of Topography to Friction by Sliding Experiments

Value addition to coconut - opportunities and challenges.

Optimization of friction stir welding parameters for precipitation hardenable aluminum alloys 7020 and 6061

The Role of Surface Texture on Friction and Transfer Layer Formation - A Study of Aluminium and Steel Pair using Pin-on-Plate Sliding Tester

Damage Mechanisms under Fretting of Self-mated Stainless Steel (SS 316L) and Chromium Carbide Coatings