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Fibers 2017, 5(1), 8; doi:10.3390/fib5010008

Modeling and Experiments on Ballistic Impact into UHMWPE Yarns Using Flat and Saddle-Nosed Projectiles

1
Sibley School of Mechanical and Aerospace Engineering, Cornell University, 321 Thurston Hall, Ithaca, NY 14853, USA
2
DSM Ahead, Materials Science Centre, 6160 MD Geleen, The Netherlands
3
DSM Dyneema, 6160 BD Geleen, The Netherlands
4
TNO, Laboratory for Ballistic Research, P.O. Box 45, 2280 Rijswijk, The Netherlands
*
Author to whom correspondence should be addressed.
Academic Editors: John W. Gillespie and Subramani Sockalingam
Received: 6 December 2016 / Revised: 3 February 2017 / Accepted: 13 February 2017 / Published: 2 March 2017
(This article belongs to the Special Issue Polymer Fibers)
View Full-Text   |   Download PDF [6017 KB, uploaded 2 March 2017]   |  

Abstract

Yarn shooting experiments were conducted to determine the ballistically-relevant, Young’s modulus and tensile strength of ultra-high molecular weight polyethylene (UHMWPE) fiber. Target specimens were Dyneema® SK76 yarns (1760 dtex), twisted to 40 turns/m, and initially tensioned to stresses ranging from 29 to 2200 MPa. Yarns were impacted, transversely, by two types of cylindrical steel projectiles at velocities ranging from 150 to 555 m/s: (i) a reverse-fired, fragment simulating projectile (FSP) where the flat rear face impacted the yarn rather than the beveled nose; and (ii) a ‘saddle-nosed projectile’ having a specially contoured nose imparting circular curvature in the region of impact, but opposite curvature transversely to prevent yarn slippage off the nose. Experimental data consisted of sequential photographic images of the progress of the triangular transverse wave, as well as tensile wave speed measured using spaced, piezo-electric sensors. Yarn Young’s modulus, calculated from the tensile wave-speed, varied from 133 GPa at minimal initial tension to 208 GPa at the highest initial tensions. However, varying projectile impact velocity, and thus, the strain jump on impact, had negligible effect on the modulus. Contrary to predictions from the classical Cole-Smith model for 1D yarn impact, the critical velocity for yarn failure differed significantly for the two projectile types, being 18% lower for the flat-faced, reversed FSP projectile compared to the saddle-nosed projectile, which converts to an apparent 25% difference in yarn strength. To explain this difference, a wave-propagation model was developed that incorporates tension wave collision under blunt impact by a flat-faced projectile, in contrast to outward wave propagation in the classical model. Agreement between experiment and model predictions was outstanding across a wide range of initial yarn tensions. However, plots of calculated failure stress versus yarn pre-tension stress resulted in apparent yarn strengths much lower than 3.4 GPa from quasi-static tension tests, although a plot of critical velocity versus initial tension did project to 3.4 GPa at zero velocity. This strength reduction (occurring also in aramid fibers) suggested that transverse fiber distortion and yarn compaction from a compressive shock wave under the projectile results in fiber-on-fiber interference in the emerging transverse wave front, causing a gradient in fiber tensile strains with depth, and strain concentration in fibers nearest the projectile face. A model was developed to illustrate the phenomenon. View Full-Text
Keywords: ballistic impact of UHMWPE yarns; dynamic Young’s modulus; shock wave collision ballistic impact of UHMWPE yarns; dynamic Young’s modulus; shock wave collision
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Phoenix, S.L.; Heisserer, U.; van der Werff, H.; van der Jagt-Deutekom, M. Modeling and Experiments on Ballistic Impact into UHMWPE Yarns Using Flat and Saddle-Nosed Projectiles. Fibers 2017, 5, 8.

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