Time Resolved Optically Based Temperature and Pressure Measurements of Suspended C-4 Spheres During and After Detonation

Report No. ARL-TR-5667
Authors: John Densmore, Matthew Biss, John Ritter, Brendan McAndrew, Barrie Homan, and Kevin McNesby
Date/Pages: August 2011; 40 pages
Abstract: Time-resolved temperature measurements of the rapidly expanding fireball resulting from the detonation of a spherical C-4 explosive charge were conducted. A multiple imaging rig consisting of a three-color integrating, two-color imaging, and fullcolor imaging pyrometer, and a wavelength-resolved integrating spectrograph was used to determine fireball surface temperatures and peak pressures. The charges were suspended at 12.7, 19.0, 31.8, 44.4, and 63.5 cm above an 8.26-cm-thick steel table, which was ~91 cm above the ground. Depending on measurement technique, peak fireball surface temperatures following detonation approached 5000 K and rapidly decayed to a steady-state temperature near 2100 K for all charges tested. Emission measurements showed the strongest discrete spectral emission was from the sodium doublet near 589 nm. Temperature traces showed that for charges closest to the table surface, the early time gas temperatures were up to 500 K higher than for charges furthest away. After shock-fireball separation, regardless of initial standoff, the fireball surface temperature decayed to a common value near 2100 K. Fireball surface/primary shockwave expansion-rate measurements approaching 4 km/s were measured from imaging-pyrometer frames. Peak shock wave pressures were found to range from 1.38 - 24.82 MPa, exhibiting an approximate inverse relationship with radial standoff distance. Total charge mass was either 227 g (29 charges) or 454 g (3 charges).
Distribution: Approved for public release
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Last Update / Reviewed: August 1, 2011