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DETONATION PROPERTIES
pressure. Th.e “acoustic approximation” is then used to calculate the corresponding
explosive pr’essure from P, = P, (pornUs + p,,D)l2p,,U,, where P, = pressure in the
explosive, P, = pressure in the inert plate, porn and pox = initial densities in the
inert plate and explosive,
velocity.
respectively, U, = shock velocity, and D = detonation
Using an assumed y-law equation of state for the explosive reaction products, one
can then calculate y = (p,,D”/P,) - 1 and U,, = Dl(r + 1).
The flash..gap technique was used to measure the inert plate’s initial free-surface
velocities. “Step blocks” of polymethylmethacrylate were mounted on the plate,
with O.l-mm-thick steel shim-covered argon flash gaps as shown in Fig. 3.01. The
explosive-accelerated inert plate closed the pair of lateral reference gaps when it
began moving, and after traversing the known free-run distance, it closed the other
identical gap. The length of this free run was selected to avoid shock reverberation
effects on the velocity. Closure of the gaps provided a brilliant, brief flash of light.
Images of the flashes were recorded by a streaking camera using multiple slits and
yielding multiple determinations of the free-run time, hence velocity. The typical
width of a flash gap along the slit length was 19 mm. The initial free-surface
velocity technique is described in more detail in “Measurement of Chapman-
Jouguet Pressure for Explosives” by W. E. Deal.’
Table 3.26 lists the detonation or Chapman-Jouguet (C-J) pressure, P,; the explosive’s
particle velocity, U,,; and the parameter of the assumed y-law equation of
state, y, folr each explosive.
Subsequent tables give densities, compositions, sample sizes, boosters, and the
detailed shock information on each explosive. In the “analysis” section of the tables,
t represents plate thickness; p, density; P, pressure; Ufs, free surface velocity; U,,
shock veloc:ity; U,, particle velocity; D, detonation velocity; and y, the parameter of
the assumed y-law equation of state. The subscript “0” refers to initial state, “x” to
explosive, and “m” to the plate material. The parameters are given for a linear least
squares fit of free-surface velocity vs plate thickness, and the corresponding explosive
parameters are derived from the acoustic approximation.
The detonation pressure has been shown to be a function of the charge geometry,
and these ‘data are omitted herein.
CAMERA “EW
1 SLIT PLATE
Fig. 3.01. Plexiglas block as-
sembly for measurement of free-
surface velocity of an explosive-
driven plate.
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