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

The effect of ultrasonic energy on the interfacial microstructure in Cu-Al bonds is investigated to establish a relationship between ultrasonic energy, interfacial structure and bonding strength. It is shown that formation of intermetallic compounds (IMCs) at a Cu/Al interface is strongly dependent on the character of ultrasonic vibration; higher levels of ultrasonic energy enhance fragmentation of an oxide layer, resulting in continuous alloy interfaces. In addition, a stronger ultrasonic vibration heats up the interface to a higher temperature, and simultaneously creates more grain boundaries and dislocations, promoting migration of metal and leading to thicker IMCs. Formation of continuous thick IMCs at the Cu/Al interface significantly improves the bonding strength.

Effect of ultrasonic energy on interfacial structure and bond strength in copper wire bonding

It has been well known that plastic deformation of bulk metallic glasses
(BMGs) is localised in thin shear bands. So, initiation of shear bands and
related deformation should be studied for comprehensive understanding of
deformation mechanisms of BMGs. In this paper, indentation techniques are
extensively used to characterise elastic deformation of Zr-Cu-based metallic
glass, followed by a systematic analysis of initiation and evolution of shear
bands in the indented materials. Our results, obtained with a suggested
wedge-indentation technique, demonstrated initiation of shear bands in materials
volume.

Indentation study of mechanical behaviour of Zr-Cu-based metallic glass

In this study, the finite element analysis is chosen to investigate the thermo-mechanical properties of an indium joint exposed to low-temperature cycling. Based on the experimental data, the computational model is built, and the material model of indium is proposed for different joint thickness. The obtained results demonstrate that the outmost corner of the interface between the small indium joint and copper substrate is the weak site, while the large indium joint is characterized by a perfectly elastic core surrounded by uniformly plastic deformation during low-temperature cycling. With the proposed material model, the package-indium bump bonding with sensor and readout, used in the photon counting pixel detector Medipix 3, was studied under conditions of low-temperature cycling. The study provides an insight into the response of joints to thermal fatigue in indium joints during low-temperature cycling.

Numerical analysis of response of indium micro-joint to low-temperature cycling

Demand for advanced engineering composites in the aerospace industry is increasing continuously. Lately, carbon fibre reinforced polymers (CFRPs) became one of the most important structural materials in the industry due to a combination of characteristics such as: excellent stiffness, high strength-to-weight ratio, and ease of manufacture according to application. In service, aerospace composite components and structures are exposed to various transient loads, some of which can propagate in them as cyclic impacts. A typical example is an effect of the wind gusts during flight. This type of loading is known as impact fatigue (IF); it is a repetition of low-energy impacts. Such loads can cause various types of damage in composites: fibre breaking, transverse matrix cracking, de-bonding between fibres and matrix and delamination resulting in reduction of residual stiffness and loss of functionality. Furthermore, this damage is often sub-surface, which reinforces the need for more regular inspection. The effects of IF are of major importance due its detrimental effect on the structural integrity of components that can be generated after relatively few impacts at low force levels compared to those in a standard fatigue regime. This study utilises an innovative testing system with the capability of subjecting specimens to a series of repetitive impacts. The primary subject of this paper is to assess the damaging effect of IF on the behaviour of drilled CFRP specimens, exposed to such loading. A detailed damage analysis is implemented utilising an X-ray micro computed tomography system. The main findings suggested that at early stages of life damage is governed by o degree splits along the length of the specimens resulting in a 20% reduction of stiffness. The final failure damage scenario indicated that transverse crasks in the 90 degree plies are the main reason for complete delamination which can be translated to a 50% stiffness reduction.

https://iopscience.iop.org/article/10.1088/1742-6596/305/1/012047/pdf

Damage assessment in CFRP laminates exposed to impact fatigue loading

Recent studies have contested long-standing assumptions that mechanical anisotropy is caused by weak interlayer bonding and demonstrated that microscale geometry (the groove between extruded filaments) is the major cause of anisotropy in extrusion additive manufacturing (AM). Inspired by those finding, this study investigates the potential for a new convention for print-path design to improve mechanical properties by setting extrusion width to be at least 250 % of nozzle diameter. The new convention enabled an almost 50 % improvement in mechanical performance, which was supported by finite element analysis data, whilst simultaneously reducing the printing time by 67 %. Whereas a typical extrusion AM part uses several side-by-side extrusions, here, three 0.4-mm-wide extrusions are replaced with a single extra-wide 1.2-mm extrusion; two 0.6-mm-wide extrusions are also studied. The contact area between layers of the extra-wide extrusion was 90 % as opposed to 63 % for the conventional approach. The improved contact area led to a 40–48 % enhancement of strength, strain-at-fracture and toughness. This study presents a compelling case for a methodological shift to extra-wide extruded-filament deposition and explains the underlying cause of anisotropic strength observed in previous studies. Two case studies demonstrate practical applicability for a print run of 1000 nylon visors and lower-limb polylactide prosthetic sockets, for which extra-wide filaments more than doubled load-bearing capabilities. Polylactide material was used for most of the study; potential for translation to other materials is discussed. 

Vadim V. Silberschmidt

Papers

Effect of ultrasonic energy on interfacial structure and bond strength in copper wire bonding

Indentation study of mechanical behaviour of Zr-Cu-based metallic glass

Numerical analysis of response of indium micro-joint to low-temperature cycling

Damage assessment in CFRP laminates exposed to impact fatigue loading

Extra-wide deposition in extrusion additive manufacturing: A new convention for improved interlayer mechanical performance