04/01/2019: Prof. Lee gave an invited talk at ACS Meeting

Prof. Lee gave an invited talk in the ACS National Meeting and Expo (Orlando, FL).


Technical Session: Materials for High-Performance Impact Mitigation: Design, Synthesis, Characterization & Validation

Impact Energy Delocalization Properties of Carbon-based Nanomaterials and Nanocomposites

Jae-Hwang Lee1* and Wanting Xie1,2

1Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, Massachusetts 01002, USA.

2Department of Physics, University of Massachusetts, Amherst, Massachusetts 01002, USA.

*E-mail: leejh@umass.edu

In a lightweight armor system, a projectile’s kinetic energy impinging on an impact point has to be immediately re-distributed through the armor layer perpendicular to the impact direction. As the initial point-like impact turns into areal impact, a threat of penetration can be mitigated without increasing a thickness of the armor system. Since this impact energy delocalization process cannot occur faster than the speed of sound of the armor material, carbon nanotubes and graphene, having the exceptionally high speeds of sound, are promising for anti-ballistic materials.

We have worked with a microscopic ballistic technique called the Laser-Induced Projectile Impact Test (LIPIT) to investigate high-strain-rate mechanical characteristics of carbon-based nanomaterials and their scalable composites. In LIPIT, a microsphere is launched to a speed as high as 1 km/s and mechanical deformation of materials subjected to the speeding microsphere is imaged by sub-picosecond light pulses, which limit motion blur to below optical resolution (~100 nanometers). Using the observations of the microspheres penetrating through free-standing multilayer graphene membranes in vacuum, impact energy delocalization properties of multilayer graphene were directly characterized without aerodynamic friction of a projectile and a membrane specimen. LIPIT was also applied to graphene-oxide/silk-fibroin nanocomposites, which is a scalable nanomaterial platform. LIPIT evidently demonstrated that percolation of the graphene-oxide phase allowed extensive impact energy delocalization. As another scalable nanomaterial platform, we also investigated wet-spun carbon nanotube fibers with LIPIT and directly compared them with Nylon and Kevlar fibers. The carbon nanotube fibers demonstrated superior impact mitigation performance due to their highest transverse wave speed arising from high-strain-rate collective interactions among carbon nanotubes.