Experimental methodology to assess the effect of coatings on fiber properties using nanoindentation

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Aguilar, Juan Pablo
Antoniou, Antonia
Stollberg, David
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Current body armor technologies need further improvements in their design to help reduce combat injuries of military and law enforcement personnel. Kevlar-based body armor systems have good ballistic resistance up to a certain ballistic threat level due to limitations such as decreased mobility and increased weight [1,2]. Kevlar fibers have been modified in this work using a nano-scale boron carbide coating and a marked increase in the puncture resistance has been experimentally observed. It is hypothesized that this improvement is due to the enhancement of the mechanical properties of the individual Kevlar fibers due to the nano-scale coatings. This study presents a comprehensive experimental investigation of individual Kevlar fibers based on nanoindentation to quantify the cause of the enhanced puncture resistance. The experimental setup was validated using copper wires with a diameter size in the same order of magnitude as Kevlar fibers. Results from nanoindentation did not show significant changes in the modulus or hardness of the Kevlar fibers. Scanning Electron Microscopy revealed that the coated fibers had a marked change in their surface morphology. The main finding of this work is that the boron carbide coating did not affect the properties of the individual fibers due to poor adhesion and non-uniformity. This implies that the observed enhancement in puncture resistance originates from the interaction between fibers due to the increase in roughness. The results are important in identifying further ways to enhance Kevlar puncture resistance by modifying the surface properties of fibers.
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