PRESSURE 
~! TIME 
33 
Fig, 16 - Pressure _on plate when there is no cavitation at plate or in water 
Fig. 16 illustrates the pressure/time variation of equation 31 
diagrammatically and shows that the pressure acting on the plate will 
be initially 2p, which corresponds to instantaneous complete reflection 
The pressure then decreases to zero, followed by negative values 
which will ultimately tend to zero asymptotically. 
87. This occurrence of tensions between the water and the plate raises 
immediately the question as to whether any appreciable tension can in 
fact be sustained between water and paint or steel. Further, if the 
preceding theory were correct, after tension develops between the plate 
and the water, there will also be tension in the water for some distance 
away from the plate. Can water withstand these tensions? Moreover, 
even if the water does not break, can it exert an appreciable tension 
on the plate? The answers to these questions, affect vitally the whole 
problem of damage to air-backed plates by the pressure pulse. Three 
cases will be considered: - 
(4) The water sticks to the plate and does not cavitate. 
(2) The water cannot exert any tension on the plate, but does not 
itself cavitate. 
(3) The water cannot exert any tension on the plate and itself 
cavitates after the plate leaves the water. 
Water sticks to plate and does not cavitate 
88. Equation 30 holds for any value of time and the maximum value of 
the displacement, which occurs when + becomes infinitely large, is given 
by 
2D, 2p, 
= SO OCR mide. Meco | conn cosa, (ED, 
