729 
Par eee 
For spherical shock waves the energy factor calculated from [ee dt does 
not include the entire shock wave energy. A better approximation to this is 
given by the /Pi/P dt} dt. This takes into account the after-flow correction 
due to the spherical form of the wave, which may amount to as much as 25 pere 
cent of the value of the energy factor at distances of less than 20 charge 
radii.l/ ‘Hence the energy calculated from /'Pé dt which is reported for 
RELIANCE results is referred to as the "energy factor." 
(e) General comments concerning piezoelectric instrumentation, The 
rather comprehensive information concerning the pressure-time rclationships 
resulting from an underwater explosion which can be obtained by the use of 
piezoelectric gauges is invaluable but at the same time requires much work 
and infinite patience when compared to the ease with which results may be 
obtained from mechanical, gauges, To maintain 6 channels in operating con— 
dition the following personnel requirements must be met: maintenance and 
repair of gauges and cables, 3 semi-skilled persons; checking and operating 
equipment on board vessel, 1 technician (college training or equivalent ) 
with help from cable men; development, construction, repair, maintenance, 
and laboratory checking of electronics equipment, 1 to 3 college~trained 
electronicians; analysis of piezoelectric records and working up results, 
1 college girl with major in mathematics or physics and 2 assistants with 
college training; supervision of all work, correlating field work, laboratory 
work, and record reading, trouble shooting, planning and execution of ex— 
periments, 1 college trained man experienced in electronics, physics, and 
underwater explosion phenomena, The above is the staff required for average 
loads, and- does not include scamen to set the charge and gear. Under peak 
loads additional help is necessary. 
8, The UERL diaphragm gauge 
The first gauge to be successfully uscd at this laboratory for compar= 
ing explosives was the UERL diaphragm gauge [1,5,20] (Fig. 19)¢ 
(a) Description. -- This gauge is constructed by welding a 3—in. 
length of j-in., double extra strong steel pipe (finished to an inner diam 
eter of 3.270 in.) to a square base of 1/2—in. plate. A top plate in which 
there is a hole of the same diameter as the inner diameter of the pipe is 
‘welded on. A copper or stcel diaphragm is then placed over this top plate, 
a cover plate slipped over the diaphragm, held in place by 8 cap screws. 
Diaphragms which have been used have been of No. 1) B and S gauge electro-— 
lytic copper, No. 20 and No, 1) U.S. standard gauge hot-rolled steel, The 
ll-gauge steel diaphragms were the ones commonly used, the tensile strength 
being about 60,000 Ib/ins Small variations in the thickness of the stecl 
made it necessary to correct all deformations to a standard thiclmess of 
0.085 in. Thickness corrections were made according to Kirkwood theory, 
and later according to empirical results obtained during shooting with 
small charges. 
(b) Measurement of explosive effectiveness, — The relative effective- 
ness of various explosives is measured with the diaphragm gauge in terms of 
the maximum depression of the steel diaphragm caused by the shock wave. The 
Th, B. Arons, private communication. 
