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Using gas-gun-driven plate impact techniques, we have measured the Hugoniot of the filled silicone elastomer DC745U cooled to -60°C. DC745U consists of approximately 62 weight% poly-dimethyl-siloxane rubber and 38 wt% silicon dioxide filler. At ~ -50°C, the poly-dimethyl-siloxane rubber in DC745U crystallizes with ~ 40% crystallinity. This is accompanied by a density change from 1.31 g/cm³ at 23°C to 1.45 g/cm³ at -60°C. Below the crystallization transition temperature, a measurable increase in the shock velocity was observed. This is coincident with a decrease in compressibility due to crystallization of the polydimethylsiloxane repeat units. The linear US - up Hugoniot also significantly changes from US = 1:62 + 1:74up mm/µs at 23°C to US = 2:00 ± 0:05 + (2:06 ± 0:06)up mm/µs at -60°C. Cooling to -60°C and the associated crystalline phase transition therefore results in considerable stiffening. This is the first time, to our knowledge, that a polymer crystallization transition has been shown to affect shockwave properties in this way. [ABSTRACT FROM AUTHOR]

We present gas-gun driven plate impact shock initiation experiments on the explosive PBX 9502 (95 weight percent triaminotrinitrobenzene, 5 weight percent Kel-F 800 binder) heated to ∼ 76°C. PBX 9502 samples were heated by flowing hot air through a sample mounting plate and surrounding coil. Temperatures were monitored using embedded and surface mounted type-E thermocouples. The shock to detonation transition was recorded using embedded electromagnetic particle velocity gauges. Results show increased shock sensitivity; time and distance to detonation onset vs. initial shock pressure are shorter than when the sample is initially at ambient temperature. Our results are consistent with those reported by Dallman and Wackerle: the "Pop-plot," or distance to detonation, xD, vs. impact pressure, P, is log10(xD) = 3.41-2.47log10(P). [ABSTRACT FROM AUTHOR]