Effects of nanosilica on the ballistic impact tolerance of carbon/epoxy tubes loaded in torsion

Fiber reinforced polymer composites can save weight in rotorcraft structures, but have not been widely used in driveshafts due in part to their limited impact tolerance. The objective of the current investigation is to evaluate the effects of incorporating variable amounts of nanosilica (NS) particles in the matrix on the ballistic impact tolerance of carbon/epoxy tubes loaded in torsion. Tubes manufactured with these matrix materials were ballistically impacted using a round steel projectile aimed at normal incidence across the major diameter. After impact, the tubes were nondestructively inspected and subjected to mechanical tests to determine the axial and shear stiffness and the residual shear strength in torsion. In the best material formulations, which were 15 and 25 weight percent NS in epoxy, the use of NS decreased the impact damage area by 50%, increased the residual shear strength by 38%, and increased the energy absorbed per unit damage area by 120% versus the control material with no NS. Overall, the addition of NS significantly improved the impact tolerance of carbon/epoxy tubes loaded in torsion, with little change in the mass density, glass transition temperature, and elastic modulus.