Improving Electrotextile Wearability Using Stiffness Testing Methods
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Improving Electrotextile Wearability Using Stiffness Testing Methods Jeremiah Slade, Dr. Patricia Wilson, Brian Farrell, Justyna Teverovsky, Douglas Thomson, Jeremy Bowman, Marty Agpaoa-Kraus, Foster-Miller, Waltham, MA 02451, U.S.A.; Wendy Horowitz, Edward Tierney, C.M. Offray, Watsontown, PA 17777, U.S.A.; Carole Winterhalter, U.S. Army Soldier Systems, Natick RD&E Center, Natick, MA 01760-5019, U.S.A. Abstract The ability to integrate electrical functionality into textile garments is becoming increasingly desired both on the battlefield and in the work environment. In order to accomplish this, the issue of compatibility of mechanical properties between dissimilar materials needs to be addressed. Textiles are typically selected for comfort while electrical materials are chosen for superior electrical properties with secondary consideration given to properties such as flexibility. As a result many attempts to integrate electrical functionality into textiles result in stiff, unwieldy garments that have difficulty gaining user acceptance. Part of the electrotextile work done at Foster-Miller has focused on the integration of these dissimilar materials in a manner that does not degrade the wearability of the garment. Our work has included the development of textile cables that carry power and data using both electrical and optical media. In order to assess the wearability of these cables a method was needed of testing their stiffness. Several methods of measuring textile stiffness existed but did not address the many issues and material characteristics unique to conductive textiles. Experimental Details FED STD 191A-5200, also known as the ‘Hanging Heart Loop test’, was chosen to evaluate the load deflection response of our initial textile cable designs, their components and related textile goods (Figure 1). This test was originally intended for standard fabrics and webbings. As a result several modifications needed to be made to the test. •
Rather than measuring the deflection of the specimen under its own weight several deflection measurements were made as a series of weights were applied.
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The slope of the load-deflection curve was used as a measure of stiffness rather than a single deflection distance.
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Deflection measurements were made with an optical comparator rather than a ruler for added accuracy (Figure 2).
Due to the wide variety of observed load response curves it was necessary to use the following criteria when calculating stiffness. For general stiffness comparisons between all types of materials it was necessary to measure the slope over a relatively narrow deflection range (2.5” 3.0”). For stiffness measurements within a group of similar materials such as electrotextiles a wider deflection range can be used to determine stiffness (i.e. 2.0” – 3.0”). By using a wider data range we were able to get more accurate stiffness measurements (Figure 3).
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USB v1.0 #1
475
USB v1.0 #2
450 425
Range over which bus stiffness (Kb) is calculated
USB v2.0
Range over which stiffness (K) is
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