593 



This formula takes no account of increase of yield strength vith 

 cold working, plastic bending, the decrease in thickness, or the elastic 

 recovery of the diaphragm. We have calculated tensile strength by means 

 of this formula using the diaphragm thickness after deformation. These 

 data for three pressures are plotted in Figure 33. It may be noted that 

 there are large variations outside the experimental error (about 3/^) in 

 tensile strength with thickness and pressure. The negative slope for the 

 thinner diaphragms and the shift in the minimum can be qualitatively ex- 

 plained by work hardening. The positive slope \rtiich increases with de- 

 creasing pressure may be qualitatively explained by elastic recovery, 



6. Study of Errors 



Moxmting the gauges on a steel ring accounted for a reduction in the 

 standard deviation of the damage of one diaphragm from the mean of four 

 diaphragms on a shot from 5^ to less than 2^. Correspondingly, the proba- 

 ble error of the damage of one diaphragm from the mean of four diaphragms 

 was reduced from 3.k'jl> to about 1%. (Cf Section V,3,c). 



