258 



SHOCK WAVE MEASUREMENTS 



boundaries at which the particle velocity and density are discontinuous, 

 but the pressures on either side are the same. 



Similar photographs have been obtained at lower pressure levels, 

 using smaller charges and explosive flash charges or high intensity 

 stroboscopic hghts for illumination. In one such experimental two 50 

 gram charges were fired simultaneously and the intersection of the 

 shock waves photographed Avhen the shock waves were 12 inches from 



^ 24 

 9 



U 20 



3 

 </) 



UJ 16 

 a: 



Q. 



o 



O 



o 



1 



150 



100 



50 



ANGLE OF INCIDENCE cL 



Fig. 7.19 Peak pressure and time constant of pressure at the intersection of 

 two shock waves (the angle of incidence a. is half the angle between the fronts). 



the charges and the fronts made an angle of 142° at their intersection. 

 The intersecting fronts gave rise to a Mach region very similar to that 

 of Fig. 7.17, except for the increased obhquity and the fact that no 

 slipstreams were visible (possibly because of the small discontinuity in 

 velocity and density to be expected at the low pressure level). The 

 experimental value a = 71° was appreciably larger than the calculated 

 value of 55° for the experimental pressure of 11,000 Ib./in.^. The oc- 

 currence of the Mach region for this case is thus in agreement with the 

 theoretical predictions. 



" R. W. Spitzer and R. S. Price, UE 16 (114). Experiments with detonator caps 

 exploded simultaneously have been reported by Campbell (10). 



