517 

 ABSTRACT 



This report, which describes a great variety of experiments with a 

 simple type of tmderwater gauge, should be of interest to anyone concerned 

 with the damaging power of \anderwater explosions. It not only describes 

 the construction and use of this gauge for compeiring explosives but also 

 a variety of experiments which throw light on the way in ■vrtiich damage is 

 produced in structures by vmderwater explosions. It provides an illumi- 

 nating illustration of the precautions and care which are required in 

 order that accurate and precise conclusions can be drawn from even simple 

 scientific investigations. 



Principally to compare various explosives with respect to their 

 underwater damaging power and to investigate the various factors con- 

 trolling damage by underwater explosions, a type of diaphragm gauge was 

 constructed for use at this laboratory. It consisted of a circular steel 

 or copper diaphragm, about I/16 in. thick, clamped across the open end of 

 a strong steel cup, the inside diameter of which was 3.3 in. The dia- 

 phragm formed a watertight seal over the cup so that on submersion the 

 gauge remained air-filled. By exposing the gauge sxiff iciently close to 

 an underwater explosion, the diaphragm was permanently deformed; the de- 

 pression at the point of maximum deformation was measured and arbitrarily 

 defined as the damage produced. The more importeint results obtained with 

 this gaxige using small charges (up to 25 lbs.) aire outlined below. 



1. The equation D = k was found to apoly over a considerable 



range of experimental conditions. In this equation, D is the maximum 

 depression of the diaphragm, k is a constant for a given type of explosive 

 and a given type of diaphragm, W is the charge weight, d is the charge- 

 to-gauge distance, m and n are constants for a given type of diaphragm. 

 It was found experimentally that m and n for a given diaphragm material 

 were approximately in the ratio 1 to 2. For steel diaphragms, m and n 

 were found to be about 0.6 and 1.2, respectively; for copper, m sind n 

 were respectively O.k and 0.8. ~ ~ 



2. For steel diaphragms, the damages observed experimentally agreed 

 closely with those predicted by the theoretical studies of diaphragm 

 deformation carried out by J. G. Kirkwood and others. 



3. When half -scale gaxjges were exposed to underwater explosions in 

 which all other linear dimensions of the experiment were decreased by 

 one-half, the damage produced was one-half that obtained with the 

 regular gauges imder normal conditions. In other words, Hopkinson's 

 scaling rule was found to hold for a two-to-one variation. 



k. If the gauges were held in place by a simple wooden framework 

 instead of by an encompassing steel ring, the damage could be decreased 

 by as much as 50^. This was indicated to be due to rarefaction waves 

 reflected from the wood and consequent cancellation of a portion of the 

 pressure wave from the explosion. 



