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Effects of Crimp and Slip on Laminar and Woven Fabrics Subjected To Ballistic Impact

NCJ Number
Date Published
November 2013
186 pages
This study covers the growing interest about and research in improving the performance of soft body armor materials subjected to high-speed ballistic impact especially in regard to the effects of "crimp" in conjunction with yarn slip in ballistic fabrics.
One "by-product" of the production process for high strength polymer fibers, which are bundled into yarns, is the existence of undesirable undulation or waviness in the yarns, known as crimp. The authors developed a Finite-Difference (FD) numerical model to study the post-impact and pre-failure behavior of crimped fabrics made with Dyneema yarns in order to overcome weaknesses in previous studies that provide little insight into the strain profile of individual yarns, the growth and evolution of tension and cone waves, and the yarn de-crimping process. Most fabrics are woven with an interlaced, over-under yarn structure, and the authors developed a second crimp model with woven geometry. In addition to the forces from the first model, they introduced new forces to describe the contact motion between weft and warp yarns in-plane (viscoelastic), and out-of-plane (allowing for compression, but imposing a "hertzian" condition). Correspondingly, they introduced new parameters to control for yarn slip, crossover forces, and restoring forces. Comparing the two models, it was observed that the second model provides greater flexibility and is more realistic in its ability to accurately portray the phenomenon of crimp interchange. Within the woven crimp model, many of the same trends in results provided from the laminar model were seen. Also discovered was that most of the parametric effects are not independent of each other, and provide case studies to show that varying combinations of multiple parameter values can produce nearly identical simulation behavior, but in other cases significantly different simulation behavior from one another.
Date Published: November 1, 2013