Characterization of Energy Absorption of Two Armor Grade Composites Arrangements Base on Aramid and Polypropylene
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Characterization of Energy Absorption of Two Armor Grade Composites Arrangements Base on Aramid and Polypropylene R.A. Gamboa, J.G. Carrillo*, R.H. Rafful, B.J. Dzul Centro de Investigación Científica de Yucatán, A.C., Mérida, Yucatán, México. *[email protected] ABSTRACT Ballistic grade composite materials have shown several advantages in comparison with their individual constituents, such as increased ballistic limit and reduced posterior trauma. One configuration in particular that has demonstrated greater ballistic efficiency is the arrangement of independent laminates (IL). It presents an increase in energy absorption compared to its counterpart of consolidated laminates (CL). In this study, an analysis is carried out to determine the effect on the ballistic performance of IL and CL arrangements when they are subjected to biaxial prestress (BP). Results show how the ballistic advantage obtained in IL is nullified in comparison with CL, thus demonstrating the limitations of this arrangement for possible applications where the arrangement is subjected to normal impacts with BP. INTRODUCTION Armor-grade composites are characterized by a more effective ballistic performance in comparison with their individual constituents. This improvement is due to different energy absorption mechanisms resulting from the interaction of the fiber with the continuous matrix; mechanisms such as interlaminar and intralaminar delamination, and redistribution of stresses are present during an impact event [1-3]. In the literature, there is still some doubt as to the effect of biaxial prestress (BP) on the ballistic performance of armor-grade composites. For example, a study carried out by Kalamis reports that, when different composites materials laminates of fiber and thermoset resins are subjected to in-plane prestress of up to 51 kN, a substantial increase in the ballistic resistance of the material can be observed, whereas tests on material without prestress results in poorer ballistic performance [4]. Other studies have demonstrated how the integration of a polypropylene (PP) matrix to a Kevlar® 720 fabric increases the ballistic resistance of the material, due to energy dissipation mechanisms afforded by a continuous phase. Similarly, a configuration known as “independent laminates” is able to increase energy absorption by 13%, simply by modifying the production process of the Kevlar® 720 composite material [5, 6]. In the present study, a composite material based on aramid woven, Kevlar® 720 and an atactic PP matrix (K720/PP) are characterized in two configurations arrangements denominated consolidated laminate (CL) and independent laminate (IL). These two arrangements are subjected to high velocity impact tests with and without biaxial prestress (BP), with the objective to evaluate changes in energy absorption under these two holding conditions. EXPERIMENTAL DETAILS For the elaboration of the fiber/matrix arrangements, an aramid woven, Kevlar® 720, 1000 denier, 20 counts/in is used. The matrix is a 32 μm atactic PP film. Using these ma
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