586 



and the observed rise for second and third jiulses and the time of the 

 third pulse for 1 lb. of blasting gelatin2b/. Use was made of the 

 theories of Herrin g^? /. Taylor^S/, and Willis2o/ to scale these results 

 to the case in hand. The effects of the gauge itself, the surface, and 

 the bottom on the bubble motion have been ignored. 



This result confirms the results of other investigators on the 

 effect of the bubble from small charges on targets above the charge but 

 does not invalidate the earlier conclusion that UERL damage gauges 

 mounted at the same level as the charge are normally affected only by 

 the primary shock wave. 



(b) Mach effect on diaphragm damage . Damage gauges located in the 

 region of the intersection of two shock waves under conditions such that 

 Mach type interference29/ was expected, showed maximum depressions up to 

 nearly 1.5 times the maximiim depression observed when the same total 

 weight was detonated at the position midway between the positions of the 

 two equal charges producing the intersecting waves. 



The experimental arrangement is shown schematically in Figure 28. 



oc 



t^l7 



Fig 



Arrangement for testing Mach effect. 



The charges were arranged so that the line joining their centers and the 

 line between the two opposite gauges, 6 and 17, bisected each other 

 perpendicularly. 



Eqvial lengths of primacord from a No. 8 detonator were used to fire 

 the chEirges simultaneously. According to Seeger and von Neiomann (private 

 communication), the theoretical critical angle oL at which the Mach 

 effect first appears for these charge weights and charge-to-gauge distances 

 is 69°. This series covered the range from 62° to 90°. The results are 

 listed in Table XXIII. 



26/ H. F. Willis and R. T. Ackroyd, Undex 36 

 27/ Conyers Herring, NDRC c4-sr20-010, OSRD 236 

 25/ G. I. Taylor, TMB No. 510 



29/ For a discussion of this effect see P. C. Keenan and R. J. Seeger, 

 Navy BuOrd Explosives Research Report I5, Febrioary 19^^. 



