578 



to observe the effect of the size of the bending radius on the damage 

 of steel diaphragms in general, and the point of rupture in particular, 

 a gaxLge was altered to have a bending radius of l/8 in. 



Damages vere obtained ranging from l/2 in. to the bursting limit 

 and in general were .01 to .02 in. greater than for the normal gauge. 

 Steel diaphragms in the gauge with the l/8 in. radius burst in the center 

 and had a bursting limit of about 1.25 in. as compared with 1.10 in. for 

 the normal gauge. 



(h) Shape of deformation profile . Kirkwood predicts££/ 

 diaphra.gm is exposed to an impulsive shock 



that if a 



T 



Pressure 



Time 



i.e., a shock wave of very short duration relative to the diaphragm 

 deflection time, the shape of the deformation will tend to be conical. 

 On the other hand, if the diaphragm is exposed to a step shock. 



Pressure 



Time 



where the duration of the pressure is very long compared to the deflection 

 time, he predicts a spherical deformation. Ordinary shock wave diirations 

 in diaphragm gauge work fall between these two limits, but it is interest- 

 ing to note that Kirkwood 's predictions are borne out at least qualitatively 

 as these limits are approached. In Figures 25 and 26 the central profiles 

 of two sets of damaged steel diaphragms are reproduced. The maximum de- 

 flection for the diaphragms of each set are approximately equal, and the 

 change in shape of the profiles for shock waves of increasing duration is 

 evident. Thin (.O38 in.) diaphragms were chosen to demonstrate this 

 effect since sharp bends would tend to be "ironed out" by thicker diaphragms. 



Another demonstration of change of shape with wave form is clearly 

 shown in the experiments wherein the shock-wave is cut off by bringing the 

 gauges and charge successively closer to the surface (cf . Sections V. 3, a 

 and V, k, c). Here the shape becomes more conical as the cut-off time is 

 shortened. 



22/ J. G. Kirkwood and J. M. Richardson OSRD No. 4200, p.^l-O ' 



