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SHOCK INITIATION PROPERTIES
Fig. 4.02.
explosives-state locus given by the conservation-of-momentum relation for the ex-
plosive, P = pOUpUs, where U, = shock velocity and p0 = initial density. The at-
tenuator rarefaction locus is approximated by reflecting the attenuator Hugoniot
line about a line where the attenuator particle velocity is a constant. Because initia-
tion is not a steady state, the conservation-of-momentum relation does not hold
precisely; however, near the sample and attenuator interface, the reaction is slight
enough that the accuracy is sufficient. Values of the initial shock parameters, P,,
UpO, and U,,, are given in the tables that follow.
Figure 4.02 shows a typical smear camera wedge record. Characteristically, these
traces show the initial shock, the point of transition to high-order detonation, and
the high-order detonation. The space and time dimensions are shown. Although the
shock and detonation velocities in the explosive can be determined from these
records, only the coordinates for the high-order detonation, x* and t*, are normally
found. Historically, many analysis techniques have been used, including those used
here for data analysis.
THE TECHNIQUES
Technique l.‘In Technique 1, the early average shock velocity is determined from
the angle generated on the camera record by the shock-wave progress along the
wedge surface, the optical magnification, the wedge angle, the viewing angle, and
the camera writing speed. The distance over which this measurement is made is
kept as short as is practical. The distance and time of transition to high-order
detonation are determined from the film measurements, knowledge of the viewing
angle, etc. In all the techniques described here, it is assumed that the shock wave is
plane and parallel to the wedge-and-attenuator interface. The initial shock and
particle velocity vs pressure in the wedge are obtained from a graphical solution in-
volving the wedge density, early average shock velocity, and pressure in the last at-
tenuator plate.
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