445 



TIME-DISPLACEMENT STUDIES OF DIAPHRAGMS DEFORMED 

 BY EXPLOSIVE LOADING 



By G. E. Hudson and C. T, Johnson 



INTRODUCTION 



The experiments, described in TMB Report 509 (10)* in 



which a thin, circular, steel diaphragm mounted in the bottom of a steel boat 

 is attacked by a small charge of explosive, have been extended to a much wid- 

 er range of distances between charge and diaphragm. In the meantime about 

 five times as many diaphragms have been tested by the methods described, with- 

 out an essential change In the technique or the apparatus. A great deal more 

 Information has been gained, owing as much to the more detailed and more ex- 

 tended analyses of the data as to the greater number of tests. All of these 

 data and analyses will be described in a subsequent TMB report. 



The aim of the present report is to furnish to other workers on dia- 

 phragms a detailed time history of the motion of the diaphragms as observed in 

 these more recent experiments. This description covers details of the first 

 swing of the diaphragm that are not given in the previous report (10). The 

 description Includes an account of the subsequent motion and vibrations of 

 the boat after the shock wave impinges upon it, as well as an account of the 

 subsequent bulging of the diaphragm as a result of the pressure pulses emit- 

 ted from the oscillating gas globe. 



Although not all details of the motion are fully understood, at- 

 tempts are made at explanations of certain phases of it. Such explanations 

 are presented chiefly as hypotheses to be tested by further observations and 

 experiments. 



TEST APPARATUS AND PROCEDURE 



The diaphragms used in these tests were of furniture steel, having 

 a yield stress Oy of '+3.5 >< ^ 0^ pounds per square inch, and radius a of 5.125 

 inches. Their uniform Initial thickness Kq was O.0567 Inch. Each charge 

 weighed 0.8 ounce and consisted of 22 grams of tetryl plus a detonator cap. 



The diaphragms were welded at the rim to steel holding rings 1 inch 

 thick, which in turn were bolted to a mounting ring, so that the combination 

 was about 2 inches thick. The mounting ring was bolted to the bottom plate 

 of a flat-bottomed steel boat. The bottom plate of the boat was of steel 1 

 inch thick, 5 feet wide by 5 l/2 feet long. The total weight of the boat was 

 about lUoO pounds. The charges were detonated in the water beneath the boat 

 and on the axis of symmetry of the diaphragms, at distances varying from 5 

 Inches to 52 inches. All other pertinent dimensions are given in Figure 21. 



Numbers in parenthesis indicate references at the end of this paper. 



