11 
measurements when the gauge was in contact with the charge. The results 
of these experiments indicate that at close ranges (between 8 and 13 times 
the charge radius), the original empirical formulae are not strictly true and, 
therefore, revised formulae have been proposed.* In addition to fitting 
results obtained at close ranges, these revised formulae also give a better 
fit for early results. At even closer ranges, further work indicates that 
these revised formulae have to be further modified. Nevertheless, in order 
to indicate the general nature of the formulae, it is instructive to quote 
the original* empirical results for T.NeT. These results will be reasonably 
accurate for distances greater than about 100 times the charge radius. Tet 
W = weight of T.N.T. charge in lb. 
D = distance from charge in feet 
then the following empirical formulae were proposed from the early 
experimental data 
Y 
P,= a cone Soin Cobre sem Masee qicddie, Goo we Abo Mhodd “Gad saat (Ca) 
= 1.92 iy Gee meekkyeky! goo 'Gc0. coo ooo ‘Goo sde (12) 
4 
St = 28x10 Fa ft. Ibe per sqe fts soe sae cee tee woe (13) 
7 eS 7 Ds = 305 x 40 x Wft. Ib. eee eee eee eee eon (14) 
It should be emphasised that these formulae were derived from data obtained 
at distances for which -, is of order of 2 tons per sq. in. or less and are 
not accurate™ for distances closer to the charge. The outer region in which 
these formulae are applicable is the region in which the pulse should behave 
sensibly as a small amplitude wave. These empirical formulae confirm that 
the form of variation of the respective quantities p,, I and with 
distance and the constancy of E for the pulse from a given charge agrees 
with that predicted by the theoretical equations in the outer region. 
252 Since the shape of the pressure/time curve is not exactly exponential, 
it is necessary to decide which features of the actual pulse are to be most 
accurately simulated when using equation 10 to represent the pulse for 
damage purposes. . For this purpose, the quantities p., I and5< can be used 
but, in general, only two of the three equations 4, 4B and 13 can be 
accurately satisfied by a curve of the form given by equation 10 which 
involves only two parameters. 
26. If the maximm pressure be chosen as a first criterion, then equation 
11 is used to give p, in equation 10. Therefore, either equation 12 or 13 
can be used to determine an appropriate value of n for T.N.T. charges. 
27. If impulse is the second criterion to be adopted for fitting the 
experimental results by using equation 10; then from equations A15 and 10 
Eis E- eee coe eve ooo eee coe eee ceo eee eee (15) 
Hence, substituting for p, and I from equations 11 and 12 in equation 15 
45 
ahaet e 
i = $250 °° coo eee eoe eee coo eoe eee eee eee (16) 
ak 
Wy [41013 
P, = 17,570 {5} lbe per sqo in. 
4 
Toba 2.279 © Ib. sec. per sq. in. 
$2 = 30,660 ¥, ft. lb. per sq. fte 
E = 385,200 W ft. 1b. 
