EFFECT OF CONFINEMENT AND THERMAL CYCLING ON THE SHOCK INITIATION OF LX-17

The shock initiation of the insensitive high explosive LX-17, which co ntains 92.5% triaminotrinitrobenzene (TATB) and 7.5% Kel-F binder, was studied under two simulated accident conditions: initially confined c harges were heated to 250 degrees C and shocked; and unconfined charge s were thermally cycled between 25 degrees and 250 degrees C and shock ed. Previous research on unconfined TATE-based explosives heated to 25 0 degrees C revealed increased shock sensitivity. This increase was at tributed to both the increased porosity caused by the unsymmetrical th ermal expansion of TATB, which resulted in more hotspot ignition sites , and the faster growth of hot spot reactions due to the increased sur rounding temperature. In this study, aluminum confinement was used to decrease the thermal expansion of LX-17. The shock sensitivity of conf ined LX-17 at 250 degrees C was observed to be less than that of uncon fined charges at 250 degrees C but greater than that of unconfined, am bient temperature LX-17. The thermal cycling results showed that the L X-17 heated to 250 degrees C and then shocked at 25 degrees C was more sensitive than pristine LX-17, because irreversible growth had produc ed more ignition Sites. LX-17 held at 250 degrees C for an hour or fir ed at 250 degrees C after two thermal cycles did not appear to be sign ificantly more shock sensitive than LX-17 heated to 250 degrees C and shocked immediately. Therefore it is unlikely that TATE is thermally d ecomposing into less stable intermediate species at 250 degrees C. The Ignition and Growth reactive flow model for shock initiation of LX-17 was normalized to these experimental results to provide a predictive capability for other accident scenarios that cannot be tested directly .