519 



I. INTRODUCTION 



When underwater explosives research was begun by the NDRC in the 

 spring of 19'<-1, tvo of the most important tasks undertaken were (l) the 

 study of the factors which influence underwater explosion damage, and 

 (2) the comparison of various underwater explosives with respect to 

 their damaging power. Since "damage" is a loosely defined term, there 

 can be no such instrument as a "damage gauge"; yet, there could be no 

 solution to the above mentioned problems without some means, arbitrary 

 though it may be, of measuring damage. Accordingly, in the summer of 

 19^1, a gauge consisting of a strong steel cylinder, closed at one end, 

 and covered at the other end with a relatively thin metal diaphragm was 

 put into use. ^>^>3 / The "damage" meastired by the gauge was the amount 

 of deformation suffered by the diaphragm on exposure to the underwater 

 explosion. 



Althovigh this gauge was an arbitrary one, it was used successfully 

 for comparison of explosives in the weight range from about one ounce 

 to 25 lbs. as well as for testing service weapons. It was of particular 

 value in the period during which the more elaborate techniques of 

 explosion measxirement were being developed. 



II. DESCRIPTION OF THE UERL DIAPHRAGM GAUGE 



1. Construction 



This diaphragm gauge was designed and constructed in 19^1 at the 

 Explosives Research Laboratory, Bruceton, Pennsylvaniai/ as follows. 

 (See Fig\ires 1 and 2.) The edges of a section of steel pipe, k-l/2 in. 

 O.D. X 3-1/8 in. I.D. X 3 in. long, were beveled for fillet welding. 

 A solid steel plate J x J x l/2 in. was welded over one end of the pipe 

 section, and the second plate "J x J x 1/2 in. with a central hole of 

 nearly 3-lA in. diameter was welded over the other end of the pipe. 

 The outside face of this second plate was milled flat, ajid the hole was 

 acctirately finished to a diameter of 3*270 in. The edge between the 

 side of the hole and the milled face was then rounded off into a 90° arc 

 of 1/16 in. radius. A third steel plate, f x J x l/2 in., was milled 

 flat on one face and a tapered hole ^.582 x 3«^32 in. bored in the 

 center, the narrower end of the hole being at the milled face. Smaller 

 holes were drilled thro\agh the two milled plates, and the holes in one 

 were tapped to take l/2 in. x 13 thread cap screws so that the two plates 

 could be bolted tightly together. Provision was made for eight cap screws 

 spaced around the main hole. The first gauges were so constructed that 

 the cap screws were inserted through the welded plate to engage threads 

 in the cover plate; this proved to be cianbersome and subsequent gauges 

 were made with holes tapped in the welded plate. A hole was drilled also 

 in each corner of the two plates so that pins could be inserted to assure 

 reproducible alignment of the two plates. 



2_' This gauge has been previously described by Fye and Alexander in 



OSRD Report No. IO35, November 191^2. 

 2/ Wilson, Cole and Fye, OSRD Report No. 1220, February 19'^3. 

 3/ A diaphragm gauge was already in use by the British, cf , Mine Design 

 - Department, Summary No. M. S. 9^oA2, A.C. 3338, October 19^2. 



