158 



MEASUREMENT OF PRESSURES 



tory at Woods Hole/ is sketched in Fig. 5.5. The diaphragm A is 

 ordinarily made of steel or copper .080 inch thick and is clamped to the 

 gauge body by a face plate, the diameter of the area exposed to pressure 

 being 3.4 inches. In practice, the gauge is placed a known distance 

 from the explosion and the resultant roughly semi-spherical depression 

 taken to be a measure of the explosive's effectiveness. As in the case 

 of the Modugno gauge the law of its motion is not a simple function of 



30 



z 

 Q 1.0 



(T 

 O 

 li- 

 UJ 



o 



-J 

 < 

 o: 



»- 

 z 



UJ 



o 



0.3 



0.1 



3 10 



CHARGE WEIGHT (LB) 



3C 



Fig. 5.6 Deformation of 3.4 inch steel diaphragms at 2 distances from small 

 charges. The sohd hnes are calculated theoretical values. 



any single property of the shock wave, and practical use of the gauge 

 has been largely for empirical comparisons. The response of the gauge 

 has, however, been used to test theoretical calculations of Kirkwood on 

 the response of simple structures to shock pressures and has given a 

 considerable amount of useful information. Half-scale gauges have 

 also been used to demonstrate for special cases the validity of an ex- 

 tension of the similarity principle to structiu'es, known as Hopkinson's 

 rule. This rule states that if all the linear dimensions of a structure and 

 the explosion to which it is subjected are scaled by a factor X, the re- 

 sultant damage will be increased in the same scale. Although the rule 



"A detailed account of results obtained with this gauge at the Underwater 

 Explosives Research Laboratory (Woods Hole) is given in a report by P. M. Fye 

 and J. E. Eldridge (39) . 



