October 10, 2018
Abstract: My group has worked with a microscopic ballistic technique called Advanced Laser-Induced Projectile Impact Test (α-LIPIT) to study high-strain-rate mechanical characteristics of various materials ranging from conventional materials to nanomaterials. In this talk, I will introduce our recent progress on the high-strain-rate study using α-LIPIT with carbon-based nanomaterials. For example, a single microfiber, spun from individual carbon nanotubes (CNTs), is an ensemble of weakly-interacting aligned nanomaterials having no scaling-up limit in length. Thus, CNT fibers can be useful constituents as high-performance mechanical materials due to the high intrinsic strength and low density of CNTs. However, 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-sphere on a CNT fiber. Three other fibers, Kevlar filaments, Nylon filaments, and pure aluminum filaments, are also investigated under the same conditions for comparison. Each fiber is mounted in air and a single glass sphere (~ 30 mm in diameter) collides 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, primarily due to the highest transverse wave speed of the CNT fibers arising from high-strain-rate collective interactions between CNTs. 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.
Jae-Hwang Lee has been an Assistant Professor in the Department of Mechanical and Industrial Engineering at University of Massachusetts Amherst since 2014. He received a PhD degree in 2006 from Iowa State University in Condensed Matter Physics for 3D photonic crystals and their thermal applications. During his postdoctoral study in the Institute for Soldier Nanotechnologies at MIT, he focused on the mechanical deformation of multi-phase periodic nanomaterials. Afterwards, he worked as a research scientist in the Richard Smalley Institute at Rice University until 2014.