Figure 19b represents the maximum effective stress in the 

 tension-tension quadrant due to the worst boundary condition, the fixed 

 case. This point always occurred at the center of the low-pressurfe face for 

 the complete range of the variables. The fixed boundary case was the worst 

 due to the increase in flexural bending. 



Example 



To indicate how the design curves may be used, a hypothetical case 

 is considered. Suppose the design requirements are as follows: 



Maximum operating pressure = 2,000 psi 



Maximum temperature = TO^F 



Safety factor = 1 .5 



Length of dive* = 100 hours 



Included angle = 90° 



Minor diameter = large as possible 



To properly design this viewport, the first step is to find out what t/d ratio 

 is necessary. From Figure 18 with an abscissa value of 100 hours, the follow- 

 ing results are obtained: 



compressive yield stress = 6,000 

 tensile yield stress = 3,000 



Proceeding to Figures 19a and 19b,and calculating the ordinate value for 

 each curve 



(p) (S.F.) (2,000(1.5) __ 



compressive = — — = 0.5 



CTy 6,000 



^ ., (p) (S.F.) (2,000) (1.5) .. 

 tensile = — — =1.0 



CTy j,000 



Using the above ordinate values, the following t/d ratios were taken off 

 the abscissa: 



from Figure 19a t/d = 0.58 

 from Figure 19b t/d = 0.34 



This assumes that there is adequate relaxation time between dives. 



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