Ramp-wave Experiments to Measure Dispersiveness in Explosives

Composite explosives such as PBX-9404\footnote{J. W. Nunziato, E. K. Walsh and J. E. Kennedy, \textit{Intl. J. Eng. Sci. }\textbf{\textit{16}}, 637, 1978.} and PBX-9501\footnote{J. J. Dick, A. R. Martinez and R. S. Hixson, \textit{Eleventh Intl. Detonation Symp}., p. 317, ONR 33300-5, 1998.} are known to disperse shock waves into ramp waves at stresses of 1.2 GPa or less. Thus a shock wave cannot propagate in those explosives at such low stresses. Ramp-wave experiments have been performed on PBX-9501 to determine the minimum stress level at which shocking up occurs. Gas-gun experiments involved impact of a projectile onto a fused-silica plate, which developed a ramp wave that was transmitted through the explosive sample. The shape of the wave exiting from the sample was measured with VISAR. The compression level at which the ramp steepens into a shock indicates the limit of the dispersive behavior. This is of interest particularly because the ramping-out behavior may reduce the vigor of response of an explosive to hazard circumstances that ignite deflagration, and thus forestall DDT.