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

THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

Effect of Temperature

Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Advanced polymeric materials, such as ultra-high molecular weight polyethylene (UHMWPE) are used in lightweight body armour because of their combination of good impact resistance with light weight. However, a broader use of such materials is limited by the complexity and cost of the manufacturing processes and the lack of experimental data on their behaviour and failure evolution under high strain-rate loading conditions. The current study deals with an investigation of the internal heat generation during the tensile testing of UHWMPE and polymer nano-composite blends at various strain rates. A 3D finite element (FE) model of the tensile test is developed and validated with the experimental work. An elastic-plastic material model is used with adiabatic heat generation. The temperature and stresses obtained with the FE analysis are found to be in a good agreement with the experimental results for UHMWPE materials. The model can be used as a simple and cost effective tool to predict the thermo-mechanical behaviour of parts made from these materials under various loading conditions.

Thermo-Mechanical Investigation of Ultra-High Molecular Weight Polyethylene for High Strain-Rate Applications

In this paper, cyclic plasticity in a single crystal nickel-based superalloy CMSX4 at elevated temperature was modelled using crystal plasticity (CP) and discrete dislocation dynamics (DDD). The CP modelling was carried out at the continuum level based on shear deformation along the octahedral slip systems. The DDD approach was implemented for a representative volume element with periodical boundary conditions. The DDD model parameters were calibrated using the predicted response by the CP model. The obtained numerical results by the two models compared with each other under strain-controlled monotonic and cyclic loading conditions in both and orientations. The CP model was further applied to study crack-tip deformation under fatigue loading. Stress-strain responses, as well as stress and strain distributions, near the crack tip were particularly monitored to assess the role of cyclic plasticity in controlling fatigue-crack propagation. The work has applications in life assessment of nickel-based superalloy components for high-temperature applications

Vadim V. Silberschmidt

Papers

Thermo-Mechanical Investigation of Ultra-High Molecular Weight Polyethylene for High Strain-Rate Applications

Modelling of cyclic plasticity and crack-tip deformation in a single crystal nickel-based superalloy