6/4/18: Prof. Lee gives a talk at SEM conference

Society for Experimental Mechanics (SEM) Annual Conference
June 4–7, 2018 at the Hyatt Regency Greenville, SC

Real-time Observation of Ballistic Deformation of Single CNT and Kevlar Filaments
Jae-Hwang Lee^1*,Wanting Xie^1,2, Robert Headrick³, Runyang Zhang⁴, Lauren Taylor³, Matteo Pasquali³, Sinan Müftü⁴

Carbon nanotubes (CNTs) are promising constituents as high-performance mechanical materials due to the high intrinsic strength and low density. CNTs 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 high-strain-rate performance of CNT fibers.

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 mm in dia.) is mounted in air using two epoxy supports and individual glass spheres (~ 30 mm 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 impact mitigation performance to the other three fibers, including Kevlar KM2, primarily due to the highest transverse wave speed of the CNT fibers. Scanning electron microscopy 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.