The Effect of Weaving on the Strength of Kevlar KM2 Single Fibers at Different Loading Rates

NOTICES Disclaimers The findings in this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. Citation of manufacturer's or trade names does not constitute an official endorsement or approval of the use thereof. Destroy this report when it is no longer needed. Do not return it to the originator. Approved for public release; distribution is unlimited. Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. Understanding the mechanical behavior of woven Kevlar fibers at high loading rates is needed to develop material models that mathematically represent the deformation and failure for computer codes that are being developed or used to simulate high– loading-rate events such as impact on fiber-based protective items. When fibers are woven into fabric, they may get damaged, thus reducing their strength. In order to understand the effect of weaving on the strength of Kevlar fabric, individual fibers from both the warp and weft directions must be studied. In this experimental study, the strengths of warp and weft fibers from plain-woven Kevlar KM2 fabric, as well as unwoven virgin fibers, are measured and compared to quantify any damage due to weaving. The fiber responses are evaluated at low, intermediate, and high strain rates, with 5-mm-gauge-length samples. Low-and intermediate-rate mechanical deformation experiments are conducted using the Bose ElectroForce test system, and the corresponding high-rate experiments are conducted using a split Hopkinson tension bar modified for fiber characterization. This report presents a comparison of strengths of woven fibers with that of unwoven fibers to determine the possible degradation of strength at different loading rates due to weaving.