562 



(ii) Experimental results . For the experimental work baffles of 

 three different radii were used in conjunction with regular UERL damage 

 gauges and baffles of four different types were used with half-scale 

 gauges . 



Tests with the regular gauges axe summarized in Table XIV. The 

 baffles were cut out of 1 in. steel armor plate with a square hole at 

 the center for the gauge; the baffle and gauge were rigidly held to- 

 gether by inch-thick steel bars bolted on in back so that the front 

 face of the gauge and the baffle-face were one plane surface without 

 obstructions except for the heads of the gauge cap screws. Two baffled 

 gauges were fastened opposite each other at the points spaced 90° from 

 the unbaffled, control gauges. All gauges were mounted in the usual 

 fashion on a steel ring. 



A 12 in. radius baffle was made and tried first. Since it was 

 feared that the large area exposed to the shock wave might cause the 

 ring to be pushed out of shape, small charges were first tried before 

 using the size charge for which calculations were made. It was found 

 on the contrary that the ring was pulled in (toward the explosion) along 

 the axis of the baffles. Since the ring was distorted by each shot, 

 the experiment was carried on by moving all gauges 90° around the ring 

 after each shot to get the baffled gauges on the long axis and reverse 

 the distortion. A distance correction was applied using distances to 

 the charge before the shot; this correction is valid only if damage is 

 completed before distortion occurs. The correction for both baffled 

 and unbaffled gauges was made by using the distance exponent (l.2l) as 

 determined with the \mbaffled gauges. It gave consistent results when 

 used in addition to the thickness correction (Sec. V, h, a), and two 

 shots in which wire cable was run across the ring to decrease the dis- 

 torting motion showed no difference in resiilts. To find out if possible 

 diffraction through the crack between gauge euid baffle had einy effect, 

 two shots were fired with the crack plugged with lead and sealed with 

 "Bostik" (a rubber cement); there was no difference in resiilts. 



With 8 in. radius baffles, the same distortion occurred to a 

 smaller extent; the method used was the same and the results were treated 

 in the same way. Two shots in which the crack between gavige and beiffle 

 was covered with sheet steel showed no difference in results. 



Infinite baffles were obtained by using a baffle with a 2'4- in. 

 radius (well beyond the theoretical limiting radius), and by placing 

 gauges, with and without baffles, flush with the sandy bottom of the 

 ocean. In the latter case, the charge was supported kd in. above the 

 gauge. A special rig was necessary to force the gauge and baffle down 

 until the face was flush with the bottom, and a diver had to examine 

 the gauge and set the charge on its support. Results were not very 

 reproducible because the charge distance was uncertain, the gauge could 

 not be set perfectly flush with the bottom, and the bottom itself was 

 not perfectly reproducible. 



