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CURATOR
A pinboard by
Christian Sorensen

Graduate Research Fellow, Purdue University

PINBOARD SUMMARY

Hot spots are the best theory for how explosions start, I engineer these individually in crystals

Hot spot theory for the initiation of energetic materials (explosives) says that because a single shock compression wave traveling across a material doesn't account for the subsequent initiation of that explosive, there must be some sort of energy localization. There are many candidates for the points at which energy (and so higher temperatures) is localized; some include adiabatic heating, pore collapse, viscoelastic (heating from non-destructive deformation), viscoplastic (heating from plastic, destructive, deformation), crack-tip heating, and various forms of shear friction modes. Perhaps all of these modes have a part to play in the process of detonation ... and in the soup of multi-crystalline particles with voids and defects, it's hard to tell what is going on.

Which brings me to the work I will present. Low-defect (near perfect) explosive crystals have been grown and had engineered defects re-inserted. It's a shame I can't include pictures because they are quite beautiful. Defects can include holes and slots formed by our miniature drill press, or fast pulsed (femtosecond) laser. Additionally, low defect crystals can be arranged to impact each other, with the knowledge that no internal flaws are contributing to the recorded outcome.

This knowledge can be used to create models for both the more efficient use of energetic materials (mining operations, etc.), and for better explosives safety (high-performance rocket propellant sometimes has a propensity to detonate under the right conditions).

7 ITEMS PINNED

Corner turning and shock desensitization experiments plus numerical modeling of detonation waves in the triaminotrinitrobenzene based explosive LX-17.

Abstract: Five new experiments are reported that tested both detonation wave corner turning and shock desensitization properties of the triaminotrinitrobenzene (TATB) based plastic bonded explosive (PBX) LX-17. These experiments used small pentaerythritol tetranitrate (PETN) charges to initiate hemispherical ultrafine TATB (UF TATB) boosters, which then initiated LX-17 hemispherical detonations. The UF TATB boosters were placed under steel shadow plates embedded in the LX-17 cylindrical charges, which were covered by thin aluminum plates. The LX-17 detonation waves propagated outward until they reached the aluminum plates, which were instrumented with photonic Doppler velocimetry probes to measure their axial free surface velocities. X-ray radiographs and framing camera images were taken at various times. The LX-17 detonations propagated around the two corners of the steel shadow plates and into thin LX-17 layers placed between the steel and the top aluminum plates. The detonation waves were met there by weak diverging shocks that propagated through the steel plates and imparted 1-2 GPa pressures to these unreacted LX-17 layers. These weak shock waves compressed and desensitized the unreacted LX-17, resulting in failures of the LX-17 detonation waves. The hydrodynamics of double corner turning and shock desensitization in the five experiments were modeled in two dimensions using the Ignition and Growth LX-17 detonation reactive flow model. The calculated arrival times and axial free surface velocity histories of the top aluminum plates were in excellent agreement with the experimental measurements.

Pub.: 10 Feb '10, Pinned: 03 Jul '17