Karan Shah

Date of Award

Spring 2021

Document Type

Open Access Thesis

Department

Computer Science and Engineering

First Advisor

Subramani Sockalingam

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) Dyneema® SK-76 fibers are widely used in personnel protection systems. Transverse ballistic impact onto these fibers results in complex multiaxial deformation modes such as axial tension, axial compression, transverse compression, and transverse shear. Previous impact studies on high performance yarns and quasi-static transverse loading of single fibers using different indenter geometries show premature failure of yarns and single fiber caused by the degradation of tensile failure strain due to the presence of such multi-axial deformation modes. However, there is a dearth of failure criterion in the literature for ballistic applications that considers the contribution of multi-axial stress or strains induced by transverse impact. This work lays the foundation towards developing a multi-axial failure criterion that can better predict ballistic performance of a material. Quasi-static transverse loading experiments are conducted on Dyneema® SK-76 single yarn at different starting angles (5°,10°,15°, and 25°) and using four different indenter geometries: round (radius of curvature (ROC) = 3.8 mm), intermediate (ROC = 0.2 mm), sharp (ROC = 0.02 mm) and razor blade (ROC = 0.002 mm). Experimental results show that for round and intermediate indenter, the yarn fails mainly in tension whereas for sharp indenter and razor blade the yarns fails via cutting or transverse shear and in a progressive manner. There is a significant degradation in the tensile failure strain for sharp indenter (0.73%) and razor blade (0.6-0.7%) compared to uniaxial tension (3.1%). However, the failure strain is approximately constant for all the angles considered. 3D finite element models are developed to investigate the degree of multi-axial loading and strain concentration developed in the yarn due to transverse loading by round projectile and sharp indenter. Finite element results for yarn loaded by sharp indenter show that transverse shear strains are dominant in the yarn-projectile contact zone and may significantly contribute towards the failure of the yarn.

Rights

© 2021, Karan Shah

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