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Some Advances in Understanding of Environmental Fatigue

A research program has yielded advances in understanding of numerous aspects of environmental crack propagation in aerospace aluminum alloys. From one perspective, the objective of this program was to quantitatively establish governing crack-tip-mechanics conditions and damage mechanisms pertinent to environmental crack propagation, using a combination of (1) high-spatial-resolution experimentation and (2) computational simulation based on continuum-mechanics mathematical models employing multiple length scales. From a slightly different perspective, the central goals of this research were to (1) develop means of accurate prediction of crack-tip stresses and plastic strains for incorporation into micromechanical descriptions of crack growth, (2) validate crack-tip-mechanics models by means of high-spatial-resolution experiments, and (3) resolve physical characteristics of damage attributable to accumulation of hydrogen at fatigue-crack tips.

Posted in: Briefs, Physical Sciences
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Cracking of Aluminum Panels Repaired With Composite Patches

An experimental study of the mechanical behavior of cracked aluminum specimens repaired with composite-material patches has yielded findings that may eventually contribute to the development of more- effective composite patches and of techniques for predicting and detecting failures in composite-patched aluminum aircraft panels. Some prior studies have addressed various aspects of composite-patch repair of aluminum specimens, but until now, little attention has been given to such important aspects of mechanical behavior and properties as the relationships among stress, strain, and growth of cracks through-out the lifetimes of specimens. In this study, effects of initiation and growth of cracks on the residual strengths of the patched specimens were characterized. This study established a correlation among damage modes, residual strengths, and evolution of strain inside and outside the patched areas.

Posted in: Briefs, Physical Sciences
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Tool for Processing and Displaying Genomics Data in Spreadsheets

ChromaBlast is a computer program that facilitates and accelerates processing and display of data by use of Microsoft Excel or other spreadsheet software that affords similar capabilities. The development of ChromaBlast was prompted by a need for improved means of analyzing and reviewing massive data sets produced in genomics and microarray-based gene-expression experiments. ChromaBlast is also generally applicable to other data sets that are amenable to spreadsheet representation.

Posted in: Briefs, Software
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Silicon Nanowires for Anodes of Rechargeable Li Power Cells

Silicon nanowires have been investigated as alternatives to the graphite heretofore widely used as an anode material in rechargeable lithium-ion power cells. The theoretical specific charge capacity of graphite, corresponding to the maximum Li content (at a composition of LiC6) is 372 mA•hr/g. In contrast, the theoretical specific charge capacity of Si corresponding to the maximum Li content (at a composition of Li4.4Si) is much greater — 4.2 A•hr/g. In previous studies in which thin films of silicon on substrates were investigated for use as high-capacity anodes, it was found that charge capacities faded rapidly in charge/discharge cycling because large changes in volume (as much as 310 percent) associated with insertion and extraction of lithium ions caused cracking and crumbling of the films, as well as delamination of the films from the substrates. The basic idea of the present nanowire approach is to disperse the active anode material into regions having small volumes in order to reduce the sizes of the changes in volume in order to reduce the adverse effects of those changes.

Posted in: Briefs, Materials
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Composites Containing Nanostructured Shape-Memory Alloys

A continuing program of research is devoted to understanding composite materials that include nanostructured shape-memory alloy (SMA) constituents and to developing methods of fabricating components from such materials. This research is intended to improve the utilization of SMAs in microscopic structures and miniaturized devices.

Posted in: Briefs, Materials
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Films Containing Nanostructures and/or Reactive Scavengers

Several advances have been made in research in the art of tailoring polymeric films to be, variously, (1) much more effective as barriers to diffusion of liquids and gases than they would otherwise be or (2) porous, with pore sizes suitable for filtration of selected gases or liquids. The part of the research addressing the barrier problem has provided a scientific basis for reducing the permeabilities of paints and packaging films to small fractions of the permeabilities of corresponding paints and packaging materials now in common use. In this part of the research, consideration was given to two strategies, described below, that can be used separately or together.

Posted in: Briefs, Materials
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Software Virtual Networks Integrate Training and Operation of Wireless Net-Centric Warfare Systems

Military planners are aggressively developing network-centric warfare platforms that use wireless communications as a force multiplier. The aim of these programs is to provide warfighters with the best equipment and technology to achieve tactical dominance as soon as practical.

Posted in: Briefs, Information Technology
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Magnetic Memory Devices for Embedded Computing

A program of research has been dedicated to the development of magnetic memory devices than can be incorporated into complementary metal oxide/semiconductor (CMOS) integrated circuits, wherein these devices can be made to function as radiation- hard logic elements and as components of small random-access memories. The goal of this development was not to provide for large-scale, bulk memories, but, instead, to provide for latches and flip-flops that can serve as state and data registers for sequential logic and as configuration registers for configurable logic. A major benefit afforded by these devices is the ability to retain the logical state of a subsystem that contains the devices when turning off the power to that subsystem to save energy until operation of the subsystem is required. The subsystem can then be powered up and begin operating within a time of the order of milliseconds.

Posted in: Briefs, Electronics & Computers
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Hybrid Micro-Electro-Mechanically Tunable Optical Filter

A prototype hybrid micro-electro- mechanically tunable optical filter (MEM-TF) based partly on an electrostatic-actuation principle has been built and tested as an essential component needed for the further development of a prototype micro-electro- mechanically tunable vertical- cavity surface emitting laser (MT-VCSEL). In turn, MT-VCSELs are needed as essential controllable-wavelength sources in diverse advanced optoelectronic devices and systems including, for example, wavelength-division multiplexers in fiber-optic communication systems; lightweight, compact, portable spectroscopic instruments for detecting chemical and biological warfare agents; holographic memory devices; fiber-optic sensors; optoelectronic signal-processing systems; and remote-sensing systems. The development of the prototype MEM-TF also has additional significance in that it demonstrates the merit of the hybrid approach (in comparison with the monolithic-integration approach) to design and fabrication of some advanced optoelectronic devices.

Posted in: Briefs, Photonics
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Interview with Ray Alderman, Executive Director of VITA

Founded in 1984 to promote VMEbus technology, VITA is a non-profit organization of more than 125 vendor companies who share a common interest in real-time, modular embedded computing systems. In August 2008, VITA's Executive Director, Ray Alderman, agreed to speak with Embedded Technology's editor, Bruce Bennett, about the state of VME technology in 2008, how far it has come in its 30-year history, and where it is likely to go in the future.

Posted in: Articles, Articles, Electronics & Computers, Embedded software, People and personalities
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