High-strain-rate mechanical characterization of nanomaterials via micro-ballistics

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Date/Time:Thursday, 25 Apr 2013 - Thursday, 25 Apr 2013
Location:PHYSICS Hall Room 5
Channel:Condensed Matter Physics
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Jae-Hwang Lee Department of Mechanical Engineering and Materials Science, Rice University

The mechanical behavior of nanomaterials under very high-strain-rate (HSR) deformation has not been extensively explored, despite HSR characterization being crucial to the development of advanced protective materials for defense and aviation. As the strain rate becomes on the order of 10^5 s^-1 or higher, material response cannot be simply predicted because of the increased influence of previously negligible nonlinear effects. Therefore, mechanical characterization of nanomaterials by common techniques, such as nanoindentation or atomic force microscopy, is inadequate for HSR characterization due to their very slow rate, while conventional ballistic testing is too bulky for most nano-materials.
In order to assess the HSR mechanical characteristics of nanomaterials, we recently introduced a micro-ballistic approach, capable of applying mechanical deformations in very localized regions with a high strain rate up to 10^9 s^-1. In micro-ballistic analysis, a micro-projectile (diameter ~3.7 micrometer) is accelerated to a high speed (up to 4 km/s) by use of a pulsed laser, and a nanomaterial target is deformed by impact of the projectile. The kinetic energy of the micro-projectile is explicitly determined by three consecutive images during flight (corresponding to 100 million frames per second). We have applied our micro-ballistic technique extensively to various material systems to broaden the understanding of nanoscale mechanisms governing macroscopic HSR behavior. In addition to experimental details of our approach, I will highlight findings from three ongoing topics: (1) the energy dissipation mechanism of a semi-infinite polymer composite consisting of alternating 20 nm thick layers of glassy and rubbery polymer; (2) penetration characteristics of extremely thin, free-standing multilayer graphene films and gold films; (3) non-equilibrium dynamic metallurgy during the collision of a single crystal silver micro-cube and a semi-infinite indium layer.