Formation of Gaps at the Specimen-Bar Interfaces in Numerical Simulations of Compression Hopkinson Bar Tests on Soft, Nearly Incompressible Materials

Report No. ARL-TR-5301
Authors: Mike Scheidler and Martin N. Raftenberg
Date/Pages: September 2010; 122 pages
Abstract: Numerical simulations of compression Hopkinson bar tests on soft, nearly incompressible materials were performed in an effort to understand inertial effects in these tests. The specimen was modeled as either a linear elastic or a nonlinear elastic solid; the nonlinear model was calibrated to ballistic gelatin data. The simulations revealed a previously unreported phenomenon, namely, for sufficiently high strain rates in the specimen and sufficiently short rise times to the final strain rate, small gaps formed at both the specimen-incident bar and the specimen-transmission bar interfaces. The size of these gaps ranged from sub-micron to as large as 43 µm. Gaps formed at small specimen strains but persisted out to large strains, closing and re-opening multiple times. At some instants the gaps extended over most of the face of the specimen. Unloading of the specimen and the pressure bars accompanied these gaps. In an effort to rule out numerical artifacts, the sensitivity of these results to mesh size and contact algorithm parameters was studied.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2010