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The shock response of periodically layered active and reactive composites

  • Author(s): Roberts, Christopher
  • Advisor(s): Lynch, Christopher
  • Yang, Jenn-Ming
  • et al.
Abstract

The propagation of shock waves through layered heterogeneous materials is fundamentally different than that of homogeneous materials. The shock front is reflected at the impedance-mismatched interfaces, creating multiple scattering events that alter the shock propagation characteristics. These effects can be utilized in shock mitigation systems, but are inherently passive. Incorporation of active materials such as piezoelectric/ferroelectric ceramics holds promise for tailoring the shock response of layered composites in real time. Mechanical energy from the shock wave is converted into electrical energy, which can then be propagated ahead of the shock front to power additional active or reactive layers.

This dissertation explores the shock response of active and reactive composites through a combination of experimental and computational work. High-strain rate testing of ferroelectric PZT 52/48 and 95/5 ceramics and periodically layered brass/ferroelectric composites were performed using a load frame, split Hopkinson pressure bar, and flyer plate impact experiments. Computational modeling of these systems was performed using the multiphysics shock code ALEGRA-FE. Additionally, a laser-driven shock compression system was used in combination with electron microscopy to study the shock response of periodically layered aluminum/nickel reactive materials deposited onto copper nanopillars.

The computational results of this work indicate that the electromechanical coupling of piezo/ferroelectric materials and their composites hold promise in tuning their shock response in real time. However, the experimental results indicate that the shock response is dominated by impact conditions such as impact velocity and composite geometry. The electrical power released by the transient loading of PZT 52/48 and 95/5 was dependent on the loading rate, and the wave speed and rise time within periodically layered active composites was dominated by impact velocity. The laser-driven shock compression system enabled the microstructure of reactive material nanopillars to be studied pre- and post-shock loading. The results indicate that laser-driven shock compression initiated layer interdiffusion, a precursor to ignition. This suggests that the laser-driven shock compression system can serve as a high throughput, low cost test bed for reactive and energetic material systems and their composites.

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