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

Compacted graphite iron (CGI) has gained significant attention in automotive industry applications thanks to its superior thermomechanical properties and competitive price. Its main fracture mechanism at the microscale—interfacial damage and debonding between graphite inclusions and a metallic matrix—can happen under high-temperature service conditions as a result of a mismatch in the coefficients of thermal expansion between the two phases of CGI. Macroscopic fracture in cast iron components can be initiated by interfacial damage at the microscale under thermomechanical load. This phenomenon was investigated in various composites but still lacks information for CGI, with its complex morphology of graphite inclusions. This research focuses on the effect of this morphology on the thermomechanical performance of CGI under high temperatures. A set of three-dimensional finite-element models was created, with a unit cell containing a single graphite inclusion embedded in a cubic domain of the metallic matrix. Elastoplastic behaviour was assumed for both phases in numerical simulations. The effect of graphite morphology on the thermomechanical performance of CGI was investigated for pure thermal loading, focusing on a high-temperature response of its constituents. The results can provide a deeper understanding of the correlation between graphite morphology and CGI fracture mechanisms under high temperatures.

/pdf/effect-of-graphite-morphology-on-the-thermomechanical-mhogodv2.pdf

Effect of Graphite Morphology on the Thermomechanical Performance of Compacted Graphite Iron

Fibre-reinforced polymers (FRPs) became one of the most important structural materials in various industries due to their unique combination of properties such as excellent stiffness, high strength-to-weight ratio, and ease to manufacture shapes tailored for applications. Hence, they are now broadly used in aerospace and naval structures as well as in automotive, construction and energy industry; there is an increasing use of them in sports products. In service, components and structures, containing composites, can be exposed to different loading conditions including dynamic events, e.g. impacts. Such loads can cause deterioration of their structural integrity and load-bearing capacity due to induced damage. Because of their heterogeneity and microstructure, composite laminates usually demonstrate multiple modes of damage and fracture if compared with more traditional, macroscopically homogeneous, structural materials such as metals and alloys. This study deals with analysis of damage in two types of fibre-reinforced polymers - cross-ply and woven laminates - under impact loading. The first type of FRP is exposed to conditions of impact fatigue (IF). IF can be defined as a repetition of low-energy impacts with energy amplitudes insufficient to cause a total failure of a component in a single impact. Another type of laminate - reinforced with 2/2 twill fabric - was loaded in various modes. The properties of, and damage evolution in, the studied two types of laminates were analysed using a combination of mechanical testing and microstructural and damage studies using optical microscopy and X-ray micro computed tomography. Dynamic mechanical tests on cross-ply laminates were implemented using a uni-axial tensile impact loading. Advanced FE models were developed in Abaqus/Explicit to characterise the response of FRP laminates to impact loading conditions in order to elucidate their dynamical mechanical behaviour. A 3d finite-element model for uni-axial tensional impact loading of tested samples of FRP cross-ply laminates was developed with a hammer-specimen interaction simulated directly to obtain detailed information about impact conditions. The obtained results are compared with experimental data.

/pdf/damage-in-fibre-reinforced-laminates-under-dynamic-loading-pgzsslnist.pdf

Damage in fibre-reinforced laminates under dynamic loading

Modelling of micromachining is a challenging but much-needed task of modern science and technology era. In this chapter, salient issues related to modelling are illustrated through some case studies of machining of single-crystal material. Two micro-scale machining processes of a single-crystal metal—conventional machining (CM) and ultrasonically assisted machining (UAM)—are investigated using a crystal-plasticity-based approach. Differences between CM and UAM are elucidated employing three case studies with different cutting velocities. The emphasis of this research is placed on a comparison of the levels of cutting force, chip morphology and dissipated plastic energy between CM and UAM. The simulation results indicate that respective improvements of UAM compared to CM depend significantly on a ratio of the nominal velocity to a critical oscillatory speed. This study ultimately enhanced the understanding of micro-mechanisms, inherent in UAM at the micro-scale.

Simulations of Machining Processes at Small Spatio-temporal Scales

Shear damage development under constant stress is studied on the basis of the analytical solution of kinetic equations of damage accumulation. The existence of two threshold stresses is linked with the presence of three various stress intervals and respective regimes of damage growth. Utilization of the limit value of damage level as the failure criterion allows the scaling of the time-to-failure to be analyzed. The effect of initial damage on failure development is investigated.

Analysis of Shear Damage Evolution

The use of fibre-reinforced plastics (FRPs) in various industrial applications continues to increase thanks to their good strength-to-weight ratio and impact resistance, as well as the high strength that provides engineers with advanced options for the design of modern structures subjected to a variety of out-of-plane impacts. An assessment of the damage morphology under such conditions using non-destructive techniques could provide useful data for material design and optimisation. This study investigated the damage mechanism and energy-absorption characteristics of E-glass laminates and sandwich structures with GFRP face sheets with PVC cores under quasi-static indentation with conical, square, and hemispherical indenters. An acoustic emission (AE) technique, coupled with a k-means++ pattern-recognition algorithm, was employed to identify the dominant microscopic and macroscopic damage mechanisms. Additionally, a post-mortem damage assessment was performed with X-ray micro computed tomography and scanning electron microscopy to validate the identified clusters. It was found that the specific energy absorption after impact with the square and hemispherical indenters of the GFRP sandwich and the plain laminate differed significantly, by 19.29% and 43.33%, respectively, while a minimal difference of 3.5% was recorded for the conical indenter. Additionally, the results obtained with the clustering technique applied to the acoustic emission signals detected the main damaged modes, such as matrix cracking, fibre/matrix debonding, delamination, the debonding of face sheets/core, and core failure. The results therefore could provide a methodology for the optimisation and prediction of damage for the health monitoring of composites.

Vadim V. Silberschmidt

Papers

Effect of Graphite Morphology on the Thermomechanical Performance of Compacted Graphite Iron

Damage in fibre-reinforced laminates under dynamic loading

Simulations of Machining Processes at Small Spatio-temporal Scales

Analysis of Shear Damage Evolution

Damage Assessment of Glass-Fibre-Reinforced Plastic Structures under Quasi-Static Indentation with Acoustic Emission