UHMWPE composites for ballistic impact resistant applications

• Main Author: Mohammad Faiz Mohammad Zulkifli
• Other Authors: Hu Xiao
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/152180
• Institution: Nanyang Technological University

Lightweight, high ballistic limit and low back-face signatures (BFS) upon impact are highly desirable performance measurements in the engineering of ballistic protection. On top of these characteristics, ballistic applications often need to be structurally sound with high stiffness and high yield strength. The complex and myriad performance demands of ballistic applications make selecting the proper materials challenging. In the engineering of ballistic protective articles primarily using fibrous laminates, factors affecting ballistic limit and failure responses in the scope of intraply and interply hybridisation has not been studied extensively. Connected with this topic, the study on the effect of positioning of add-on materials in a ballistic article are still relevant. This research work investigates the effects of material hybridisation of an ultrahigh molecular weight polyethylene (UHMWPE) fibre-based hard ballistic panel with carbon fibre, specifically for its low and high velocity impact responses. UHMWPE fibres possess unique mechanical properties such as high strength-to-weight ratio and high strain to fracture that make it a suitable candidate for use in ballistic applications. However, it is limited as a stand-alone material in structurally demanding environments due to its weak compressive and shear strength. A secondary material such as carbon fibre will be mainly used due to its highly synergistic properties such as its high strength and stiffness in tension and compression which will complement the UHMWPE fibre. Mechanical three-point bending, and ballistic tests will be used to provide a mechanistic understanding of the static and dynamic responses of the hybrid ballistic panel. The relevance of this research topic was demonstrated through the utilisation of the principles of beam bending and fibrous responses to impact. This thesis investigates developing an innovative approach of intra- and interlayering hybridisation by unravelling key differences positioning of add-on materials make particularly upon impact. The reduction in back face deformation because of such hybridisation techniques thus aids in the development and design of ballistic articles to reduce fatal injuries to end users like military and law enforcement personnel. Through this research, unexpected effects simply by varying the positions of small amounts of carbon fibre layers within an UHMWPE panel through an only interlayer hybridisation technique were observed. Positive hybrid effects such as a 30% reduction in back-face signature (BFS) with a more than two times improvement in flexural properties were seen when homogeneous carbon fibre layers were added to the UHMWPE panel. An intra- and interlayer dual hybridization type method also yielded positive outcomes when tested against falling dart test to simulate low velocity impact. The intralayer hybrid woven fabric consisting of UHMWPE and carbon fiber (PE-C) yielded interesting results in reducing BFS when added onto the UHMWPE panel. Front or back-facing PE-C hybrid had resulted in a substantial 25% reduction in BFS compared to neat UHMWPE panel. Adding PE-C hybrid fabric altered the impact failure mechanism. The added stiffness from the carbon fiber prevented excessive bending while the ductile UHMWPE fiber absorbed energy and prevented the layer from failing catastrophically. The combined effects of both materials proved to be beneficial in coping with impact events. Interestingly, to design effective ballistic protective articles, its overall softness and stiffness play a crucial role in the outcome of its performance against impact. Too stiff and the material fails catastrophically; whilst too soft and the BFS becomes too great. Managing these two parameters remain an interesting engineering dilemma when it comes to fabricating ballistic resistive article. In addition, factors such as layer survivability play a crucial role in energy absorption and failure mechanism of the overall equipment and thus affect its performance. This thesis seeks to highlight the different responses of a hybrid panel of UHMWPE and carbon fibre as well as suggest design considerations in the engineering of ballistic resistive articles.