728 
ee SB Oes 
step. This gives a good average setting. However, for measuring peak pres— 
sure a downward correction corresponding to the difference between the set- 
ting of the step and the value for the step at t = O must be made. The peak 
pressure read directly from the Harp projection is always high due to this 
factor. This illustrates another value of using the Q-step calibration since 
the cable response, being the same for the pressure record as it is for the 
step record, is taken into account in reading the pressure, impulse, and 
ener gye 
(iit) The mechanical evaluation of the impulse and energy integrals. 
Even with Harp records the integration of the pressure—time curve for impulse 
and energy by the trapezoidal approximation was still a time-consuming 
precess, Linear planimeters were available for evaluating the impulse, but 
quadrate planimeters for the energy integral were not available. For this 
reason a mechanical integrator which would simultaneously evaluate both the 
impulse and energy functions under the pressure~time curve was designed and 
constructed [18]. By the use of this integrator the impulse and energy in- 
tervals may be rapidly evaluated using either the Harp projection, or the 
original film in conjunction with an internally contained projector. 
(iv) General considerations of the integration of pressure-time 
curvese The question as to how far out on the time axis the integration 
should be carried is one which can be answered only by compromise, Since 
most of the RELIANCE work was done for the purpose of comparing explosive 
effectiveness, it has been felt that the amount of energy or impulse de- 
livered in a time comparable with the time of damage of the target is the 
important factor, For this reason the pressure-time curves were integrated 
to some constant time value which was the same for all of the particular 
charges being compared in a given series. The value used was usually from 
‘to 8 times the time constant of the shock wave. Integration to these 
times included almost all of the energy in the shock wave but did not in- 
clude nearly so large a proportion of the impulse. This integration to a 
constant time could not be used where it was desired to obtain similitude 
curves for the different explosives, For this purpose _it was necessary to 
obtain the time constant for the particular value of wt 2/R involved and to 
integrate to some exact mul tiple of this value. The time constant must be 
taken from the curve of efit versus w1/3/R, which is the best line drawn 
through values from all charges and gauges of a given series. Otherwise 
errors due to the low precision in measuring the time constant will exag- 
gerate the errors in impulse and energy being integrated. 
The integral [pe dt is transformed into the energy of the shock wave 
by means of the factor A/poCo»e The quantity A is 
6 
Nee es 6 7 x, 10 12 52 
Pm beg x 10 ae 
while Q0Co = 5658 x 0.0065T, where T (°C) is the temperature of the sea 
water, valid for T = O to 20° [19], 
