164 



Historical Background 



In connection with the torpedo-protection program which was conducted at the Taylor 

 Model Basin, U. S. Navy, during the V/ar, detailed studies were made of the daiaage done by 

 underwater explosions to thin metal circular diaphragms, air-backed, and held rigidly at 

 their peripheries. The idea was, that if an adequate description and explanation of the 

 phenomena attendant on the damage to such an apparently simple structure could be obtained, 

 some progress toward an understanding of damage produced similarly in more complex structures 

 might be made. At the same time smaller metal diaphragms were used by several other 

 research groups as underwater gauges for estimating from their deformations the relative 

 strengths of underwater explosions. These investigations led to certain theoretical develop- 

 ments along this line but from a point of view different from that taken in this article.* 

 On a later occasion, the necessity arose for the development of a simple mechanical gauge 

 to measure the velocities acquired impulsively by large structures when they are subjected 

 to a very great force of very brief duration. For this purpose, a small thin lead diaphragm 

 was mounted in a rigid closed container which was then attached to a given structure. 

 When an impulsive velocity was imparted to the structure, normal to the plane of the 

 diaphragm, the diaphragm container moved and the diaphragm material tended to remain behind. 

 The resulting deform-'tion was of course the same as if thu diaphragm itself had suddenly had 

 impressed on it an equal but opposite uniform velocity normal to its plane while the 

 container remained fixed. The theory presented in this article was developed in an attempt 

 to describe the observed motion and deformation of metal diaphragms under some of the 

 conditions encountered in these experiments and v,'ith these instruments. 

 Observations of Deformation of Diaphragms 



Vftien a thin metal diaphragm is held rigidly at its periphery, and a 

 sufficiently large uniform velocity is suddenly imparted to it perpendicular to its 

 initial plane, the following phenomena have been observed. As soon as 



*See , for example, J.G. Kirkwood and J.li. Richardson, "The plastic deformation of circular 

 diaphragms under dynamic loading by an underwater explosion wave", OSRD A200 (,194ij). This 

 unclassified report is a summary of most of the work presented in two earlier reports by 

 Kirkwoo', OGlffl 793, and llli, also declassified. 



