11/29/17: Wanting presents at MRS Boston

Wanting Xie ^{1 2} , Robert Headrick ³ , Lauren Tayler ³ , Matteo Pasquali ³ , Jae-Hwang Lee ^1 
1 Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, Massachusetts, United States, ²Department of Physics, University of Massachusetts, Amherst, Massachusetts, United States, ³ Department of Chemistry, Rice University, Houston, Texas, United States

Armor performance of ballistic fabrics is primarily dependent on the intrinsic characteristics of the individual fibers of the fabrics. Because carbon nanotubes (CNT) have displayed high strength and stiffness combined with low density, they are very promising, with much higher theoretical tensile strength over polymeric fibers. Up to now, mechanical tests on CNT fibers have mostly been within the quasi-static regime, which is inadequate for assessing the armor performance of CNT fibers. For the first time, we demonstrate supersonic impacts of a micro-projectile on a CNT fiber. Three other fibers, Kevlar KM2 filaments, Nylon 6,6 filaments, and pure aluminum filaments, are also investigated under the same conditions for comparison. The fiber (~10 um in dia.) is mounted in air using two epoxy supports and individual glass spheres (~ 30 um in dia.) impact on the fiber perpendicular to the fiber’s axial direction at ~500 m/s. The real-time deformation process is recorded using an ultrafast microscopic imaging system for accurate kinetic information of the impacting micro-projectiles and the responding fiber. We observe the characteristic V-shape deformation of each fiber during the impact, and measure instantaneous velocity and acceleration of the projectile. In terms of the specific energy dissipation rate of the micro-projectile interacting with the fiber, the CNT fibers demonstrate superior armor performance to the other three fibers, including Kevlar KM2, primarily due to the highest transverse wave speed of the CNT fibers. Scanning electron microscopy (SEM) is used to study the post-impact damage features of the fibers. For the CNT fibers, Raman spectroscopy mapping is used to reveal the impact-induced lattice damage of CNTs.