PHOTOGRAPHY OF UNDERWATER EXPLOSIONS 227 



Photographic studies of the damage process in structures are very 

 useful in an understanding of the important phenomena. Measure- 

 ments of deformation as a function of time have been carried out by 

 several groups, one of the more important conclusions from such investi- 

 gations being the demonstration of the importance of secondary bubble 

 pulses in causing damage under favorable conditions. A time history 

 of deformation is obviously a first requirement in such studies, and a 

 motion picture record is the best single method of obtaining such infor- 

 mation. As illustrations of such work, there may be mentioned studies 

 at the Taylor Model Basin by Hudson (48) on ten inch circular dia- 

 phragms, in which displacements were measured by reflection of light 

 into a moving film camera from small steel balls or aluminum spots on 

 the diaphragm. A number of photographic studies on cylinders of 

 various sizes and internal supporting structure have been made by 

 Decius and Fye (26) at Woods Hole, which have shown very strikingly 

 the importance of later bubble pulses in ultimate damage. For more 

 detailed accounts of such investigations reference should be made to the 

 original reports. 



