567 



In all tests the contact closed within a few milliseconds although 

 the secondary pulse came very much later. There was some chatter but the 

 time at which the final closure occurred was still only a fraction of the 

 bubble period. For some of the 250 gm. charges a piezoelectric gauge 

 alongside the damage gauge recorded the primary and secondary pulses as 

 a rough check on the time interval. This interval was of the order of 

 165 msec. 



This experiment was repeated using wooden frames instead of the steel 

 ring as a mounting for the gauges. The same result was obtained, i.e., the 

 damage was produced by the shock wave. 



Next, a series of measurements of the deformation of steel diaphragms 

 in UERL damage gauges on a steel ring versus time after incidence of the 

 primary shock wave was made, so that an empirical deformation -time cxurve 

 co\ald be obtained. The experimental arrangement was similar to that used 

 previously, a contact being placed known distances behind the diaphragm. 

 When closed, this contact connected a step voltage to a single sweep 

 oscillograph. The contact was sufficiently yielding that it had no ap- 

 preciable effect on the final damage. The pressure-time CTirve of the 

 explosion wave was recorded simultaneously by a piezoelectric gaxige placed 

 at the same distance from the charge (30 in. from 250 gm. loose tetryl). 

 In this way, closing of the contact produced a sharp cutoff of the 

 piezo gavige record. The circuit is shown in Figxire 20, 



zf 





C 



R, 



Oscill eg raph 



C. 



1 



_*^ 



^- E 



P - Piezoelectric gauge 

 R, - 0.3 or 20 megohms 

 Rg - 5000 ohms 



E 



6 volts 



C - Contact behind the damace ECiuga 

 C-, - Cable capacity of about 5000 /u.yu.f 

 Cg - Paddinc capacity of about 2000 ytyc^f 



Fig. 20. Circuit employed for determination of tL-nes of defomatlon. 



