735 
Oe 
(b) Measurement of deformation. —- The Bureau of Ships recomnends (12] 
that the diaphragm deformation be measured in the gauge by talcing the dif- 
ference between the position of the center of the diaphragm before and after 
the shot. While this was done for all RELIANCE shots, "out-of-gauge" read= 
ings of deformation were also made by placing a depth gauge across the edges 
of the deformed plate and moasuring the maximum depression. Ovt-of=gauge | 
readings were consistently lower than in-gauge readings, but the precision 
of the reading was not markedly different. For the comparison of explosives 
the out-of-gauge readings were equivalent to in-gauge readings, arid are much 
more convenient since it was not necessary they be made in the field nor 
need the gauges be carried back and forth to the laboratory. 
(i) Precision, The lModugno gauge is about as precise as the ball- 
crusher gauge; that is, the standard deviation per gauge per shot is 2 to 
3 percent, calculated from differences between the two members of a pair 
of gauges. However, because of the greater difficulty in handling Modugno 
gauges over ball-crusher gauges, they cannot be uscd in as great numbers 
and therefore the. same degree of precision is not so easily attainable as 
with crusher gaugese 
(c) Weight and distance exponents. — For eaceny copper disks, the 
distance exponent is 1.0, and the weight exponent 0.3.42 
11, Hilliar-type gauges 
(a) General theory. -- During World War I, Hilliar developed in England 
a mechanical gauge which would integrate the pressure—time curve over a 
range of times [12], In this gauge a free piston was accelerated by the 
force due to the pressure of the water shock wave. Aftcr travelling a given 
distance this piston struck a copper cylinder, The kinctie cnergy of the 
piston at the moment of impact could then be calculated from the deformation 
of the copper cylinder, The impulse of the water shock wave transferred to 
the piston up until the time of impeect was then determined frem thc relation- 
ship, 
Gi =< vox VB 
where I = the momentum of the water shock wave 
M = the mast of the piston 
g = the acceleration duc to gravity 
A = the area of the face of the piston 
E = the energy corresponding to the deformation of the copper cylinder. 
The time t over which the gauge integrated is cqual to the time of travel of 
the piston, This may be represented by t # L M/g I A, where Lis the length 
of travel. 
—‘See Sec. 
seg ee 
= 5(b). 
