Quantifying Damage at Multiple Loading Rates to Kevlar KM2 Fibers Due to Weaving and Finishing
Final rept. Feb 2012-Feb 2013
ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE
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Numerical simulation of impact events on fabric-based protective systems requires accurate mechanical characterization of the constituent material at similar strain rates as the impact event. Because Kevlar Kevlar is a registered trademark of DuPont Company yarn is woven into fabric to make protective equipment, the strength of the individual filaments may become compromised as a result of the crimping, weaving process, or finishing process. To elucidate and quantify any damage to the fibers as a result of the weaving or post treatment finishing process, single fibers were extracted from the warp and weft directions of plain woven, hydrophobically treated Kevlar cloth and the strength was measured over a wide range of strain rates and compared to the response of fibers extracted from an unwoven yarn. The tensile strength of fibers from the warp, weft, and unwoven Kevlar were evaluated at 0.001 s 1, 1 s 1, and approximately 1000 s 1 using a Bose Electroforce test setup and a Hopkinson tension bar modified for fiber experiments. A wide range of gage lengths from 2 to 150 mm was investigated to find the effect of defect distribution on the tensile strength of the single fibers. The results show that fibers taken from the weft direction of the woven fabric decreased in strength 3 8 compared to the unwoven fiber. The warp fibers were a minimum of 20 weaker than unwoven and weft fibers at all loading rates. Measured Young s Modulus as a function of strain rate and tensile strength as a function of gage length are also presented in this technical report.