17 

 Hencky-Von Mises failure criterion to predict the pressure at which 



the "effective stress" 0. reaches the yield strength <3 of the material. 



The appropriate collapse criterion can be derived from 



■= (a - a } + (a - a } + (a - a ] 

 vZxcp (pr rx_ 



nV2 



E a 



y 



(179) 



so that once the stresses, Equation (178), are substituted into Equation 

 (179), the following expression for the collapse pressure is obtained: 



Pc = 



h/E 



y ' 



4 ^ l+c( 



l+o( 2 



+ t 



- 1 



n PA 



(180) 



where 



A, _ K - E 



f o i 



:i8i) 



If we accept thin-shell theory as a valid starting point, then it appears 

 that the choice of thicker walled pressure-hull structures of the future 

 will depend to a large measure on the ease with which they can be econom- 

 ically fabricated. In cases of hulls requiring thicknesses of plating up to, 

 say, about 6 inches, and/or materials which are not easily fabricable and 

 weldable, the conventional construction techniques associated with the 

 monolithic cylindrical shell stiffened by the usual type of transverse ring- 

 frames is no longer practical. Recourse must therefore be had to new 

 and, as yet, untried hull concepts and constructions. It is highly possible 

 that the pressure-hull structure of the future will look like the configuration 

 shown in Figure 21. This shows the composite or sheathed concept 

 applied to either a conventional ring -stiffened cylinder or to a sandwich 



cylinder. 



121 



