1129 
9. Pressure, Impulse, and Energy Measurements 
The values for the initial pressure (p,) for gauge positions 
A, B, and C, and for the final pressure (Pp for gauge positions 
A and B, are plotted as a function of distance in Fig. 8. The dash-dot 
line shows for comparison the corresponding pressures from a spherical 
charge. Also, as mentioned previously, pressures at position A are 
about 20-40% lower than those at position B, and at both A and B the 
pressures are several fold lower than at position C. This is, of 
course, in part due to the way in which the various r's have been 
defined, 
At position C, close #8 the charge the slope approaches the 
Rice-Ginnell theoretical6»7 slope for an infinitely long line 
charge with infinite detonation velocity; at greater distances, the 
slope approaches that for spherical charges,1,2,9) and is also at 
about the same absolute level. Even though the theoretical slope for 
line charges is in good agreement with the measured limiting slope 
close to the charge, it does not agree in absolute level, being about 
30% higher than for a single-ended detonated charge and about 30% 
below a double-ended detonated charge. As the Rice-Ginnell theory 
assumes infinite detonation velocity, and it is reasonable to 
suppose that a double-ended charge approximates infinite detonation 
velocity more closely than a single-ended charge, it would appear that 
the theory would be even more than 30% below such experimental data 
as might be used to check it. (Note that although the data are plotted 
as p vs W1/3/r as is usually done for similitude, actually only 50 lb 
charges were fired. The relation found probably should hold for 
charges of different weights, provided the ratio of charge length to 
diameter were kept the same.) 
The reduced impulse is plotted against W1/3/r (W = 50 lb) in 
Fig. 9. This impulse was obtained by integrating over roughly the 
interval tp - tj. Also plotted is the reduced impulse for spherical 
INT charges, the integration time being 6.70, where 9 is the time 
constant of the shock wave. In contrast with the pressure measurements, 
impulse measurements do not differ radically from one another. Con- 
sidering the fact that the pressure-time curves were integrated over the 
interval tp - t;, which differed for positions and methods of detonation, 
the data indicates that the total shock-wave impulse is about the same 
for the different conditions and not widely different from that of a 
spherical charge. Since from acoustic theory the pressures at 
positions A and B are in the ratio p,/pp = (c - v)/(c + v), and the 
durations are in the opposite ratio (tp - ty) ,/(te - ti), =(e+v)/(c - v), 
the tmpulse should be virtually the same at A and B, when T, 7 Tp- The 
apparent agreement in absolute level with the reduced impulse for spherical 
charges plotted in Fig. 9 is partly fortuitous, owing to the arbitrary 
times of integration. 
Reduced energy is plotted against wl/3/r for 50 1b charges in 
Fig. 10 and the same remarks made about pressure and impulse with regard 
to weight, integration times, etc., apply equally well here. 
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