563 



In a supplementary experiment, a few thin (.025 in.) diaphragms 

 were damaged in the regvilar type gauge and with a 25 in. baffle, hung 

 free. The increase in damage with the baffle was 22^. 



The work with the half -scale dsunage gauges (Cf . Sec. V, 3, <3) is 

 summarized in Table XV. According to the theory, baffle radii scale with 

 gauge size, and the 8 in. and 10 in, radius baffles for the half-scale 

 gauges are about at the theoretical limit for an infinite baffle. In 

 general, the infinite baffle produced a 25^ to 30^ increase over the 

 damage occurring with the gauge alone. 



In a special experiment to obtain an infinite baffle all parts of 

 which would be reached by the shock wave at the same time, a hemispherical 

 baffle (l/8 in. thick) of 1? in. radius was used with a half-scale gauge 

 at the pole and the charge at the center. Eight shots were fired 

 {k shots of ^1 gm. loose tetryl, k of 95 gm. tetryl; charge distance 

 15 to 17 in.) with this baffle, and for comparison, six shots were fired 

 using the same charges and distances with the unbafflid gauge. The in- 

 crease in damage over the unbaffled gauge was about 205^. 



(iii) Comparison of theory with experiment . The ratio of the 

 maximum deflection in the case of the infinite free baffle to that in 

 the case of no baffle is predicted by the theoretical treatment given 

 in (V, 5, (b), i) to be Ll^i-, calculated on the assumption that regiilar 

 damage gauges are used, with Lot 3 diaphragms, and a baffle 1 in. thick, 

 and that the charge consists of BUO gra. TNT placed kQ in. from the gauge. 

 The experimental ratio found for these conditions is about 1.22 (Table 

 XIV-A) . The discrepancy may possibly be ascribed to a small departure 

 of the motion of the part of the baffle near the gauge pot from free 

 plate motion due to bending resistance, causing the value calculated 

 theoretically to be too small. 



(c) The time required for the diaphragm deformation . Kirkwood's 

 theoretical work has predicted among other results the deformation of a 

 diaphragm exposed to an tmderwater explosion wave as a function of time 

 for various experimental conditions. The empirical determination of the 

 time required for diaphragm deformation as applied to UESL damage gauges 

 will be discussed here. (Cf. also Sec. V, 3, &)• 



To determine if the secondary pulse from the second bubble expansion 

 was responsible for any appreciable fraction of the depression of a 

 diaphragm under normal use of the damage gauge, experiments were carried 

 out using an electrical contact inside the gauge and arranged to close 

 a circuit when about 90^ of the final depression was attained. The 

 circuit was connected to a cathode-ray oscillograph with a time base 

 triggered by the break of the circuit in the detonator cap of the charge. 

 Lot 3 steel diaphragms (.075 to .O85 in. thick) were used and the gauge 

 was mounted on a steel ring. 



In one set of shots, a single dummy gauge was mounted opposite the 

 gauge used. The charges were of loose tetryl (lOO gm. at I8 in., 250 gm. 

 at 6-l/h in., and 250 gm. at ca. 30 in.) and the rig was lowered to a 

 depth of about 8 ft. for firing. The total depth was 20 ft. in the other 

 shots, 2200 gm. cast TNT was employed at a distance of 7 ft. and depths 

 of 20 and 25 ft. In this case, three dumray gauges were fastened to the 

 ring. The total depth was roughly 70 ft. 



