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SHOCK INITIATION PROPERTIES
each shot, the shock wave trajectory measured back from the transition to high-
order detonation and superimposing the plots using the transition as a fiducial.
Detonation velocities are obtained from x-t data measured in the high-order region.
Technique 5. In Technique 5, the driving plate free-surface velocity always is
measured with electrical pin contactors. Buildup data from all experiments on a
given density of explosive are pooled on the assumption of a single curve buildup
and are fitted by the least squares method to the empirical function,
D = A1T(l-*3) [1 - exp (-A2TA3)] + (A/, - A1A2)T ,
where D is the distance to detonation, T is the time to detonation at any point on
the buildup curve, A, is the detonation velocity, and A,, A,, and A, are arbitrary
constants. The shock velocities are evaluated from the derivative of the above func-
tion,
u so = A1(l - A3)T-*3 b - exp (-AZTA3)] + A1A2A3 exp (-A2TA3) + Ai - A1A2 ,
using the coefficients fitted to the pooled data and the time to detonation, T = t*,
observed in the individual experiments. This shock velocity value is then used with
the driving plate free-surface velocity determined as before.
Technique 6. In Technique 6, a flash gap consisting of grooved Lucite blocks is
used to measure the driving plate free-surface velocity. Also, shock velocities are
determined by reading the average slopes from the streak records. Samples thus
analyzed had two phase-velocity regions, the normal high-order detonation and an
intermediate velocity region. The two abrupt changes in phase velocity are read
from the streak records to give the distance to the intermediate region and the dis-
tance to detonation. All other analysis is done using Technique 5.
Technique 7. In Technique 7, the x-t data are digitized into 70 discrete points. A
linear fit is made to three adjacent x-t points, and the slope is taken as the velocity
at the midpoint of the line. Then one x-t end point is dropped, a new one is added on
the other end, a new linear fit is made, and the velocity is found. This running linear
least squares process is repeated until all 70 x-t points have been used. The u-x data
are then extrapolated to zero thickness (x = 0) to find the initial shock velocity, U,,.
All other analysis is done as in Technique 1.
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