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

https://figshare.com/articles/journal_contribution/Numerical_modelling_of_size_effects_in_micro-cutting_of_f_c_c_single_crystal_Influence_of_strain_gradients/19093580/1/files/33935162.pdf

Numerical modelling of size effects in micro-cutting of f.c.c. single crystal: Influence of strain gradients

Generation and propagation of macroscopic joints in brittle rocks depend on the evolution of defects and their interaction with cracks. The proposed approach accounts for damage accumulation and joint—damage interaction in terms of local stress intensity factors (SIF). The numerical simulation of the joint’s development in the 2D region is carried out for the various kinds of the rock stochasticity. It is shown that the fractal dimension of the crack front is the invariant of the joints’ propagation process: the fractal dimension increases with the uniformity of the material properties distribution.

Fractal Characteristics of Joint Development in Stochastic Rocks

Nature creates composite materials with complex hierarchical structures that possess impressive mechanical properties enhancement capabilities. An approach to improve mechanical properties of conventional composites is to mimic the biological material structured ‘hard’ core and ‘soft’ matrix system. This would allow the efficient transfer of load stress, dissipation of energy and resistance to cracking in the composite. In the current study, reactive spark plasma sintering (SPS) of boron carbide B4C was carried out in a nitrogen N2 gas environment. The process created a unique core-shell structured material with the potential to form a high impact-resistant composite. Transmission electron microscopy observation of nitrided-B4C revealed the encapsulation of B4C grains by nano-layers of hexagonal-boron nitride (h-BN). The effect of the h-BN contents on hardness were measured using micro- and nano-indentation. Commercially available h-BN was also mechanically mixed and sintered with B4C to compare the effec...

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Bio-inspired structured boron carbide-boron nitride composite by reactive spark plasma sintering

Indentation experiments are extensively used to identify material properties and characterize local deformations at various length scales. In this study, we investigate the effect of repetitive indentation of a rigid indenter into a workpiece. Our aim is to obtain an in-depth understanding of the residual deformation (imprint) of the workpiece after each indentation and its effects on the consequent deformation behaviour of the workpiece. A nonlinear strain-rate sensitive material model is used to characterize the macroscopic response of the Ti15V3Cr3Al3Sn (a titanium-based beta-alloy) workpiece. Experimental results obtained in a Split-Hopkinson test provide the basis for the model setup. In order to understand thermo- mechanics of the deformation process and to study the effect of plastic strain accumulation in the workpiece after each indentation, two pertinent parameters are varied, namely, the friction coefficient between the indenter and workpiece, and the indenter angle.

Repetitive indentation of Ti-based alloys: A numerical study

This work presents the results of an experimental investigation of the mechanical properties of polyetheretherketone (PEEK) specimens additively manufactured (AM) by using fused filament fabrication with different printing parameters and subjected to postprocessing heat treatment. Standard and compact tension samples were manufactured with a different infill angle using 0.4 mm and 0.6 mm nozzle diameters. Some of the samples were subjected to heat treatment at 220 °C after manufacturing. Tensile tests were conducted to determine the values of elastic modulus, tensile strength, as well as mode-I fracture toughness and critical strain energy release rate. Tensile properties of single-thread and as-delivered filaments were also studied. It was concluded that heat treatment significantly improved the elastic properties, tensile strength and fracture toughness of the AM PEEK samples: the fracture resistance increased by 33 to 45% depending on the stacking order, while the tensile strength increased by some 45–65%, with the elasticity modulus grown by up to 20%. Strain fields induced in specimens by crack propagation were captured with a digital image correlation technique and compared with results of numerical simulations implemented with the extended finite-element method (XFEM). Conclusions on the optimal parameters of 3D printing of PEEK were made.

/pdf/effect-of-heat-treatment-on-elastic-properties-and-fracture-fnjn0ykn.pdf

Vadim V. Silberschmidt

Papers

Numerical modelling of size effects in micro-cutting of f.c.c. single crystal: Influence of strain gradients

Fractal Characteristics of Joint Development in Stochastic Rocks

Bio-inspired structured boron carbide-boron nitride composite by reactive spark plasma sintering

Repetitive indentation of Ti-based alloys: A numerical study

Effect of Heat Treatment on Elastic Properties and Fracture Toughness of Fused Filament Fabricated PEEK for Biomedical Applications