THE EFFECT OF STRAIN RATE AND PLY GEOMETRY ON THE STRESS-STRAIN PROPERTIES OF NYLON YARNS
ARMY NATICK LABS MA CLOTHING AND PERSONAL LIFE SUPPORT EQUIPMENT LAB
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The purpose of the study was to examine the changes that take place in thestress-strain behavior of plied yarns due to the differences in straining rates,and also the effects that yarn geometry has on these changes. A series of 12nylon plied yarns, representing a gradual buildup in geometric complexity, wasexamined. Ply structure was varied by twisting two, three, five and sevenstrands to various levels. A single untwisted strand was also used to providereference data representative of yarn with relatively little translationalcomplexity. Yarns were identified in terms of their ply torsion. Tensilestrength, elongation and work-to- reak were measured for all samples at strainrates of 100 and 288,000min. These properties were then compared to geometrictorsional levels. Results showed that the capability to translate forces andenergy through these yarns decreases with increases in geometric complexityunder the impact loading condition. At standard quasi-tatic loading rates,however, strength translation remains fairly stable and energy translationincreases with structure. Then the relative trends are diverging at the twotest speeds. The use of low-speed data in the design of items for high strainrate use provides an overestimation of the actual end-use performance.
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