730 
= hee 
effectiveness may also be measured in terms of volume of the depression, 
but this measurement docs not lend itself to as grcat precision and is also 
more difficult to perform, Dial=type depth gauges with a 6—in. base are used 
to measure this maximum depression to the nearest 0.001 in. During shoot- 
ing the gauges are mounted roughly face-on toward the charge, and it has 
been found that the maximum depression is not too dependent upon the angle 
of incidence of the shock wave. The tilt of the gauge awry from the charge 
must be great cnough so that the diaphragm is deformed unsymnctrically be- 
fore thé depression is affected. 
(i) Precision of results for large charges. The UBRL diaphragm gauge 
has been the most precisc gauge used by this laboratory, the standard dc- 
viation per gauge being roughly 1.5 to 2 percent (talculated from differ- 
enecs betwocn the two members of a pair of gauges). 
(c) Theory. -- The theory of the UERL diaphragm gauge has been worked 
out in detail by Kirkwood [5,21], who has also swamarized the work done on 
the problem of the plastic deformation of circular diaphragms by G I, Tay~ 
lor, Kirkwood, Goranson, and Kennard. For stcel diaphragms the equations 
given in this section which Kirkwood obtained from his parabolic treatment 
have proved to predict the maximum depression to within 5 percent of the 
value obtained experimentally. The symbols used in the equations are as 
follows: : 
Symbol Unit Definition 
Ro in. Radius of circular diaphragm 
Ao ine Thickness of diaphragm 
f° gm/em Density of diaphragm 
car tb/ine Yield stress of diaphragm 
Po em/em Density of liquid medium 
Ry in. Radius of baffle of diaphragm 
Co ft/sec Velocity of sound in the liawid 
medium 
Li Plastic frequency of the dia— 
phragm 
ne] ; msec Decay constant assuming the shock 
wave to decay exponentially 
(P = Py cWt/8, where P is the 
pressure at any time t after the 
peal pressure of the shock wave 
a) 
di Ib-=sce/in$ Impulse of the shock wave; for 
exponentially decaying shock 
waves I = Pn? 
Zr in. Maximum central deflection 
G 7 See Time of deflection 
