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go to next speaker imageJoanna Austin
Assistant Professor, Department of Aerospace Engineering, University of Illinois at Urbana-Champaign

Joanna Austin received B.E. (Mechanical and Space Engineering) and B.Sc. (Mathematics) degrees from the University of Queensland, Australia in 2006 and 2007, and M.S. and Ph.D. degrees from GALCIT in 1998 and 2003. She currently directs the Compressible Fluid Mechanics Laboratory at Illinois, where her research interests include detonation, hypervelocity flows, wave propagation, compressible geological flows, and experimental fluid mechanics. Honors and awards include the Richard Bruce Chapman award for distinguished research in hydrodynamics in the Engineering and Applied Sciences Division at Caltech, 2003, and the Young Investigator Award from the Air Force Office of Scientific Research, 2007.

Abstract: Hydrodynamic void collapse mechanisms in detonation initiation

The formation of regions of localized energy release or "hotspots" is crucial to detonation initiation in energetic materials. Hot spots are formed due to wave interaction with micro-scale and molecular-scale material heterogeneities including voids, the focus of this study. Aging, thermal stresses, and mechanical damage can potentially alter the material structure and therefore initiation characteristics, affecting both performance and safe handling. Predicting ignition is a very challenging problem due to the extremely large spectrum of length and time scales, thermo-mechanical fluid-structure coupling, and multi-species chemical kinetics. A key issue is: What are the critical physical mechanisms leading to hotspot formation and ignition spread through a distribution of voids and how can these mechanisms be included in device-scale simulations?

The hydrodynamic processes involved in void collapse have been examined through dynamic experimentation in collaboration with numerical simulations. We examine a model problem designed to illuminate physical processes occurring during the interaction of an array of voids undergoing collapse. Diagnostic techniques applied include high speed shadowgraph movies of the void collapse process and velocity field measurements in the surrounding material. Voids collapse asymmetrically with the formation of a high speed jet. Both collapse-inhibiting (shielding) and collapse-triggering effects are observed on the downstream voids. Numerical simulations are used to investigate the role of shock diffraction and focusing. We examine the issue of loading rate in cases where the wave passage time scale is comparable to the void collapse time scale.

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