Untitled - Sciencemadness Dot Org

SHOCK INITIATION PROPERTIES
Fig. 4.01. Experimental arrange-
ment for most wedge test shots.
4.1 Wedrge-Test Data. Majowicz and Jacobs,’ and Campbell, Davis, Ramsay,
and Travis? first used the wedge test to study shock initiation of solid explosives.
The test is named for the wedge-shaped explosive sample that is shocked by a
booster-anId-attenuator system as shown in Fig. 4.01. The explosive is wedge-shaped
so that the shock or detonation wave moving through it is visible along the slant
face. The slant face and flat of the sample are covered with a thin aluminized plastic
and are ill-uminated by an intense light source. A smear camera is aligned so as to
record the light reflecting from the aluminized plastic. As the shock wave proceeds
through the explosive, the motion of the explosive mass tilts the reflecting surface
on the slant face so that the light is no longer reflected into the camera. This sharp
cutoff of light gives a well-defined record of the shock or detonation location vs time.
Usually, the shock wave appears to travel through the explosive sample at a slightly
increasing velocity and then to travel at a significantly higher velocity when detona-
tion occurs. The point of interest is the distance into the sample, x*, or time, t*, at
which detonation occurs.
The booster-and-attenuator system is selected to provide about the desired shock
pressure in the sample wedge. In all but a few of the experiments on which data are
presented here, the booster-and-attenuator systems consisted of a plane-wave lens,
a booster explosive, and an inert metal or plastic shock attenuator. In some in-
stances, the attenuator is composed of several materials. The pressure and particle
velocity are assumed to be the same on both sides of the attenuator-and-sample in-
terface. However, because initiation is not a steady state, this boundary condition is
not precisely correct. The free-surface velocity of the attenuator is measured, and
the partic1.e velocity is assumed to be about half that. The shock Hugoniot of the at-
tenuator is assumed to be known, so the shock pressure and particle velocity in the
attenuator can be evaluated using the free-surface velocity measurement. Then, the
pressure (P) and particle velocity (U,) in the explosive sample are found by deter-
mining graphically the intersection of the attenuator rarefaction locus and the
293