Structural modification of UHMWPE fiber through hybridization and CNT reinforcement for ballistic applications

Abstract

AbstractIn the construction of an armor for ballistic protection, fibers are used in the form of a laminated composite bonded to the back of the frontal ceramic layer. The composite layer dissipates energy transmitted through the ceramic layer and controls the spall. To absorb energy locally and to spread it out fast, fibers in the composite layer must have high toughness and tensile wave speed as quantified by a primary performance index called normalizing velocity. The goal of this investigation is to increase the normalizing velocity of ultra‐high molecular weight (UHMWPE) fiber that is widely used in ballistic protection. The structure of UHMWPE is modified by hybridizing with nylon and reinforcing with carbon nanotubes. Fibers are extruded by melt‐spinning. The concentration of nylon and nanotubes is 18 and 2 wt%, respectively. After extrusion, fibers are strain‐hardened by cyclic loading to align UHMWPE molecules and nanotubes along the fiber axis. Tensile properties are determined to calculate normalizing velocity. Normalizing velocities up to 1270 m/s were obtained for the modified fiber which outperforms Spectra‐2000 and Dyneema‐SK75 by 44%–57%. Materials chemistry and structure of the fiber are investigated through differential scanning calorimetry (DSC), Raman Spectroscopy, and scanning electron microscope (SEM). It was observed that micro‐droplet formation by the nylon phase during hybridization promotes interface sliding of UHMWPE ligaments and elevates the fracture strain. Raman and SEM examination demonstrates that embedded nanotubes get aligned along the fiber axis due to strain hardening and co‐continuously deform with UHMWPE sharing the load.