Chapter 14 Influence of Dynamic Multiaxial Transverse Loading onDyneema®SK76 Single Fiber Failure Frank David Thomas, Stephen L. Alexander, C. Allan Gunnarsson, Tusit Weerasooriya, and Subramani Sockalingam Abstract The primary objective of this research is to investigate, through fundamental experiments, the dynamic multiaxial deformation, failure and strength degradation mechanisms that govern individual ballistic fiber failure. Predicting ballistic impact performance of armor systems requires an understanding of fiber failure under complex multiaxial loading conditions. This study examines the failure behavior of ultrahigh molecular weight polyethylene (UHMWPE) Dyneema® SK76 single fibers under dynamic transverse impact as a function of varying loading rates and projectile geometry. A novel single fiber transverse impact experiment is developed by modifying the Kolsky bar to characterize failure of fibers to create the foundation for a failure model. Experiments are performed with load cells at the fiber ends and with high speed imaging for determining average stresses and strains. Post-test microscopy imaging of failure surfaces are compared to determine the dominant fiber failure modes for each experimental group. Keywords UHMWPE · Ballistic impact · Transverse compression · High strain rate 14.1 Introduction Polymeric fibers such as ultra-high molecular weight polyethylene (UHMWPE) are selected for ballistic applications based on their high specific stiffness and specific strength [1, 2]. Characterization of tensile properties of UHMWPE-based material systems have been performed at both quasi-static and high-rate speeds for varying length scales, ranging from single Dyneema® SK76 fibers to full woven fabrics [3, 4]. The knowledge gained through these experiments is incorporated into computer models through the multiscale mechanics of materials approach, which in turn improves predictive modeling capabilities. For ballistic performance predictions, an understanding of fiber behavior under multiaxial loading is essential. A diverse array of experiments have been performed to quantify various components of the material response of ballistic fiber to multiaxial loading, including quasi-static transverse loading of yarns and individual fibers [5], high strain rate transverse compression and measurement of single filament residual strength at quasi-static and high strain rates [6, 7], and high loading rate transverse impact of yarns [8, 9]. The quasi-static multiaxial loading has been shown to reduce the fiber tensile strength [5–7]. Experimental data combined with representative models have been applied in the development of a strain-based failure criterion for single fiber multiaxial loading at varying strain rates. However, characterizing the transverse loading behavior of individual single fibers at high strain rates is challenging. This chapter details the development of an experimental technique to characterize the failure of single fibers subjected to multiaxial loading as a function of loading rate and geometry. F. D. Thomas ( ) · S. Sockalingam McNAIR Center for Aerospace Innovation and Research, University of South Carolina, Columbia, SC, USA Department of Mechanical Engineering, University of South Carolina, Columbia, SC, USA e-mail: fthomas@email.sc.edu; SOCKALIN@mailbox.sc.edu S. L. Alexander SURVICE Engineering Company, Belcamp, MD, USA e-mail: stephen.l.alexander18.ctr@mail.mil C. A. Gunnarsson · T. Weerasooriya US Army Research Laboratory, Aberdeen Proving Ground, MD, USA e-mail: carey.a.gunnarsson.civ@mail.mil; tusit.weerasooriya.civ@mail.mil © The Society for Experimental Mechanics, Inc. 2021 S. Xia et al. (eds.), Fracture, Fatigue, Failure and Damage Evolution, Volume 3, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-60959-7_14 85
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