are used to some extent in joining cylindrical portions of different dia- 

 meters, but they constitute a small part of the total hull structure so 

 that some added strength could be allowed without a great sacrifice in 

 weight. This is also true to some extent for the closure bulkheads used 

 to terminate the cylindrical hulls. Some of the newer configurations 

 which are being considered in conjunction with the higher- strength 

 ferrous and non-ferrous materials for hulls of future deep-diving vehicles 

 will be introduced in a later section of this presentation; however, a major 

 part of our detailed discussions will be concerned with the elastic and in- 

 elastic behavior and the primary modes of collapse of ring- stiffened 

 cylindrical pressure hulls under the action of uniform hydrostatic pres- 

 sure. 



Under the action of external hydrostatic pressure, failure of a ring- 

 stiffened cylinder may be precipitated by any or a combination of three 

 basic modes. The three distinct possible modes with which we will con- 

 cern ourselves are indicated in Figure 7; they are: 



1. Axisymmetric collapse of the shell between adjacent ring frames. 



1 2 

 This has been erroneously referred to by others ' as yield failure of the 



shell, but in reality, it is a combination of yielding and axisymmetric 



buckling, or rather inelastic axisymmetric shell instability between frames . 



This mode is characterized by an accordion-type pleat which may or may 



not extend around the entire periphery, and which may or may not occur in 



more than one bay of the cylinder; a typical case is shown in Figure 8. 



10 



