Dynamics of Energetic Events in Condensed Phase Media

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Highly energetic events occur when the rate of energy release exceeds the strength of the material into which the energy is deposited. Under these conditions, the ensuing dynamics of the media is governed by compressible (nonlinear) waves such as shock waves. While these phenomena are far outside everyday experience, they play an important role in a number of natural processes and technological applications. This proposed experimental and theoretical research program will focus on three topics involving the problems and applications of the dynamics of energetic events, with an emphasis on the nonlinear wave aspects of the problems. Discrete Detonation: The propagation of detonation waves through energetic material, releasing stored energy as it propagates, is an example of a highly energetic event with important technological applications, since explosives are extensively used in mining and earth moving. Recent experimental results by the author, his colleagues, and researchers elsewhere have identified behavior of detonation waves in heterogeneous, condensed phase materials that cannot be explained by purely classical, continuum-based models of detonation wave propagation. These results suggest that phenomena occurring at the mesoscale (e.g., grains, voids, etc.) may have significant influence on the propagation of the wave. This research program will further investigate this effect experimentally as well as develop a methodology for modeling detonation propagation in media dominated by discrete, energetic events. Implosion Dynamics: The response of materials exposed to highly dynamic events is also of considerable interest. My students and I have recently undertaken a study of the dynamics of cylinders that are impulsively imploded. This work was originally motivated by the development of the hypervelocity launcher described below, but has direct relevance to approaches to harness thermonuclear fusion for power generation (i.e., inertial confinement and magnetized target fusion). We will be continuing these studies under the proposed program, focusing upon the stability of dynamically loaded converging geometries (imploding cylindrical cavities) in both solids and liquids in order to determine the limits to symmetric compression that can be achieved and the role of material properties and hydrodynamic instabilities. Hypervelocity Launcher and Impact: Another example of an energetic event is the hypervelocity impact of orbital debris or micrometeoroids on spacecraft. This mounting problem is now widely recognized due to the runaway cascade of collisions generating new debris in Earth orbit. These types of impacts occur at speeds of 7 to 70 km/s (for naturally occurring micrometeoroids), a regime that is not presently accessible in the laboratory. At impacts exceeding 10 km/s, the impact-generated pressures are sufficient to overcome the repulsion barrier between outer electron shells, giving rise to novel structural phase transitions, and upon pressure release, many engineering materials enter a region of mixed liquid and vapor states. These phenomena have not been previously studied due to their experimental inaccessibility in the laboratory. A unique hypervelocity launcher that uses explosives to dynamically implode the launcher propellant gas has recently been developed by my group at McGill, and has now demonstrated the ability to exceed the projectile velocity of conventional launchers. This research program will continue the development of the hypervelocity launcher and apply it to both fundamental problems in impact physics as well as examination of materials of interest for spacecraft shielding.