579 



(i) Thinning of diaphragms diiring deformation . The thickness of 

 the diaphragms mentioned in the preceding subsection (h) was meastired at 

 several points to determine the thinning caused by the deformation. 



Kirkwood gives the equation£^' 



o^?)^ 



(36) 



for the central thinning, where a is the thickness at the point of 

 maximum deflection, ^q i^ ^^^ initial thickness, and ^q i^ ^^^ maximum 

 deflection divided by the diaphragm radius. For diaphragms O.O38 in. 

 thick initially, the central thickness after deformation is predicted 

 from this equation to be 0.029 and 0.033 in. for central deflections of 

 0.6U and 0.46 in., respectively. Inspection of the measured thicknesses 

 indicated in Figures 25 and 26 shows reasonably good agreement between 

 theory and experiment. Kirkwood gives also an eqiiation for the thinning 

 at any other point in the deformed area. This equation requires the 

 thinning to decrease as the distance from the center is increased, 

 corresponding qualitatively with the experimental measurements. 



(j) Effect of weight and mounting . Inspection of Equations (l) 

 and (2) of Section III will show that the maximum deformation suffered 

 by a diaphragm exposed to an underwater explosion is not a function of 

 the mass of the mounting which supports it. In other words, it is 

 tacitly implied that the gauge as a whole will not move enough during 

 the time of deformation to affect the deformation significantly. The 

 independence of damage on the weight of the mounting was demonstrated 

 empirically in experiments with wooden frames (Section V, 2, 3) and also 

 in the course of some full scale weapon tests. In these tests two gauges 

 were fastened in a light (70 lb.) movmting and two gauges in a heavy 

 (220 lb.) moimting; both moxmtings were the same distance from the charge. 

 Table XX lists the mean damage ratios and the standard deviations from the 

 means. 



Table XX. Mean ratios of light mount/heavy 

 mount diaphragm depressions 



23/ OSRD No. 1^200, p. 37 



