734 
gt 
Peak pressures calculated from ball-crusher deformations, according to 
the above theory, assuming an exponentially decaying shock wave and using 
the decay constant obtained from piezoelectric=gauge results, give fairly 
good agreement with the piezoelectric peak pressures. In one series of tests 
where the gauges were mounted face=on to the charge, ball-crusher peak pres- 
sures averaged 3 percent higher than piezoelectric peak pressures. In an- 
other series of tests where the ball-crusher gauges were mounted side-on to 
the charge, ball-crusher peak pressures averaged 8 percent lower than piezo- 
electric peak pressures, The latter case covered a wide range of distances 
and the rate of decay with distance of ball-crusher peak pressures was equal 
to that of piezoelectric peak pressures within the limits of error of ob- 
servation [2,25]. 
Calculation of sphere deformation from the pressure—time curve has also 
been made by an iterative method [9], and Halverson and Slichter [10] by means 
of the superposition theorem have calculated the gauge response for shock 
waves which were not exponential. General considerations of the gauge have 
been given by Finkelstein [7], who found that the infinite baffle thickness 
for steel is from 3 to  m 
(ad) Weight and distance exponents, -- For 3/8-in. copser spheres, the 
distance exponent for gauges in the composite blocks (baffled) is 1.2, and 
for those in other mounts ee) is 1.0. Independent of the method of 
mounting the weight exponent is ony 
10. The Bureau of Ships Modugno gauge 
A diaphragm type of gauge dcveloped by the Bureau of Ships from the 
gauge described by Dr. Francesco liodugno of the Royal Italian Navy has been 
used routinely for most of the RELIANCE measurements. This gauge offers no 
particular advantages over the ball—crusher or UBRI-diaphragm gauge and is 
somewhat more difficult to use than the crusher gauge. No adequate theory 
has yet been developed for the llodugno gauges : 
(a) Description. -- The guage (Fig. 21) consists of a steel cylinder 
1-9/16 in. in diameter, in the cnd of which there is a hemispherical cavity 
of lein, radius. a circular diaphragm is placed over the end of the cylinder, 
and a cap with a circular opening l<in. in diameter is screwed over the 
diaphragm and the end of the cylinder. The flat surfaces of the cap and 
cylinder outside the hemispherical cavity have lands and grooves which aid 
in holding the diaphragm securely. The opposite end of the cylinder (below 
the spherical cavity) is machined down to a l-in. threaded stud 2+9/16 in. 
long. 
(i) Diaphra used. Diaphragm thickness varied from 0.02) to 0.067 
in. depending upon the presswre region in which the gauge was used and upon 
the material from which the diaphragm was made. Materials used were both 
soft copper and stainless steel. Each lot of disks used has been calibrated 
statically to allow corrections to be made for variations in hardness or 
tensile strength from lot to lot (Appendix VIII). 
Wace Sec. 5(b). 
