Mechanical Engineering Research Works

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Now showing 1 - 5 of 92
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    Crystal Dislocations
    (MDPI, 2016-01-06) Armstrong, Ronald W.
    Crystal dislocations were invisible until the mid-20th century although their presence had been inferred; the atomic and molecular scale dimensions had prevented earlier discovery. Now they are normally known to be just about everywhere, for example, in the softest molecularly-bonded crystals as well as within the hardest covalently-bonded diamonds. The advent of advanced techniques of atomic-scale probing has facilitated modern observations of dislocations in every crystal structure-type, particularly by X-ray diffraction topography and transmission electron microscopy. The present Special Issue provides a flavor of their ubiquitous presences, their characterizations and, especially, their influence on mechanical and electrical properties.
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    Evaluation of Batteries for Safe Air Transport
    (MDPI, 2016-05-05) Williard, Nicholas; Hendricks, Christopher; Sood, Bhanu; Chung, Jae Sik; Pecht, Michael
    Lithium-ion batteries are shipped worldwide with many limitations implemented to ensure safety and to prevent loss of cargo. Many of the transportation guidelines focus on new batteries; however, the shipment requirements for used or degraded batteries are less clear. Current international regulations regarding the air transport of lithium-ion batteries are critically reviewed. The pre-shipping tests are outlined and evaluated to assess their ability to fully mitigate risks during battery transport. In particular, the guidelines for shipping second-use batteries are considered. Because the electrochemical state of previously used batteries is inherently different from that of new batteries, additional considerations must be made to evaluate these types of cells. Additional tests are suggested that evaluate the risks of second-use batteries, which may or may not contain incipient faults.
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    Fabrication of a Miniature Paper-Based Electroosmotic Actuator
    (MDPI, 2016-11-08) Sritharan, Deepa; Smela, Elisabeth
    A voltage-controlled hydraulic actuator is presented that employs electroosmotic fluid flow (EOF) in paper microchannels within an elastomeric structure. The microfluidic device was fabricated using a new benchtop lamination process. Flexible embedded electrodes were formed from a conductive carbon-silicone composite. The pores in the layer of paper placed between the electrodes served as the microchannels for EOF, and the pumping fluid was propylene carbonate. A sealed fluid-filled chamber was formed by film-casting silicone to lay an actuating membrane over the pumping liquid. Hydraulic force generated by EOF caused the membrane to bulge by hundreds of micrometers within fractions of a second. Potential applications of these actuators include soft robots and biomedical devices.
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    Crystal Indentation Hardness
    (MDPI, 2017-01-12) Armstrong, Ronald W.; Walley, Stephen M.; Elban, Wayne L.
    There is expanded interest in the long-standing subject of the hardness properties of materials. A major part of such interest is due to the advent of nanoindentation hardness testing systems which have made available orders of magnitude increases in load and displacement measuring capabilities achieved in a continuously recorded test procedure. The new results have been smoothly merged with other advances in conventional hardness testing and with parallel developments in improved model descriptions of both elastic contact mechanics and dislocation mechanisms operative in the understanding of crystal plasticity and fracturing behaviors. No crystal is either too soft or too hard to prevent the determination of its elastic, plastic and cracking properties under a suitable probing indenter. A sampling of the wealth of measurements and reported analyses associated with the topic on a wide variety of materials are presented in the current Special Issue.
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    Safety Requirements for Transportation of Lithium Batteries
    (MDPI, 2017-06-09) Huo, Haibo; Xing, Yinjiao; Pecht, Michael; Züger, Benno J.; Khare, Neeta; Vezzini, Andrea
    The demand for battery-powered products, ranging from consumer goods to electric vehicles, keeps increasing. As a result, batteries are manufactured and shipped globally, and the safe and reliable transport of batteries from production sites to suppliers and consumers, as well as for disposal, must be guaranteed at all times. This is especially true of lithium batteries, which have been identified as dangerous goods when they are transported. This paper reviews the international and key national (U.S., Europe, China, South Korea, and Japan) air, road, rail, and sea transportation requirements for lithium batteries. This review is needed because transportation regulations are not consistent across countries and national regulations are not consistent with international regulations. Comparisons are thus provided to enable proper and cost-effective transportation; to aid in the testing, packaging, marking, labelling, and documentation required for safe and reliable lithium cell/battery transport; and to help in developing national and internal policies.