5. Measurement of Underwater 

 Explosion Pressures 



The preceding chapters have dealt with the physical and chemical 

 properties, physical laws, and mathematical developments necessary 

 to a theoretical understanding of underwater explosion processes. Be- 

 fore proceeding to a detailed comparison of the theoretical results with 

 experimental data, it is of importance to consider the techniques of 

 measurements of underwater explosion phenomena, and this chapter is 

 devoted to a brief discussion of some of the experimental methods. 

 The more important and generally applicable of these methods fall into 

 two broad classifications : mechanical and electromechanical devices for 

 pressure measurements, and optical methods, which can be applied both 

 to pressure measurements and to investigation of mass motion of the 

 water as a function of time and other variables. This chapter is con- 

 cerned with the first classification; optical methods are considered in 

 Chapter 6. 



5.1. Ckusher Gauges 



Early attempts at measurement of underwater explosion pressures 

 were all based on devices in which the basic measured effect was plastic 

 deformation of small lead or copper elements by the agency of the pres- 

 sure. Measurements of this kind provide directly only an empirical 

 comparison between different experimental conditions of charge weight, 

 distance, etc., but interpretations in terms of fundamental quantities 

 were attempted by comparing explosion effects with those of known 

 hydrostatic pressures. The earliest investigations of this kind appear 

 to be those of Abbot (1), who used w^hat is commonly described as a 

 crusher gauge, in which a steel piston acts on a small lead cylinder fixed 

 on a massive support as sketched in Fig. 5.1(a). The device may be 

 thought of as a mass (the piston) attached by a spring (the lead cylinder) 

 to a fixed support. The action of pressure on the piston face causes an 

 acceleration which is opposed by the plastic resistance of the lead to 

 deformation. The amount of deformation suffered by the cylinder is 

 then a measure of the force acting on the piston and hence of the pres- 

 sure in the surrounding fluid. In the form used by Abbot and later by 

 Schuyler, the crusher gauge is very similar to the crusher gauges used 

 in measuring pressures developed in gun barrels by propellant charges. 



The difficulty with use of such a gauge in measurement of shock 



147 



