574 



resistance of the (diaphragm) to deformation both in the elastic and 

 plastic domains." However, according to Kirkwood, a good criterion for 

 the occtirrence or non-occurrence of cavitation is the following: 



Op > Oc 



Cavitation 



eo ^Qr 



No cavitation 



where Og is equal to Rq/cq, the time required for the diffracted pressure 

 wave to travel from the periphery of the diaphragm to the center of the 

 diaphragm. (Rq is the radius of the imsupported part of the diaphragm.) 

 On this basis, "we would expect cavitation in the case of vei^ thin 

 (diaphragms) of large diameter under the impact of a wave of short duration 

 produced by a small charge of explosive." 



(iii) Proof of the existence of cavitation . To furnish an empirical 

 test of the criterion for cavitation derived theoretically, several under- 

 vater photographs^/ of about 1 microsecond exposure were taken of damage 

 gauges in the process of diaphragm deformation. A sample photograph 

 showing cavitation bubbles is reproduced in Figure 2k, and the data for 

 all photographs are siammarized in Table XVIII. 



Table XVIII - Data for cavitation photographs 



It is shown in the above table that only in one border-line case, 

 where O2 exceeds 0^ by only 2 microseconds, does the theoretical cavitation 

 criterion not apply. The figures are of course not this accurate. 



Theory and experiment both indicate that cavitation does not usually 

 occur in the use of this gauge as in this report. 



21/ J. E. Eldridge, Paul M. Fye and R. W. Spitzer, Photography of 

 Underwater Explosions I, NDRC Report A-368, OSRD 6246. 



