has been concerned chiefly with structural arrangements comprised of 

 thin sheets or facings, flat or curved, and spaced apart from each other by 

 a core of low Young's modulus material intended primarily to increase the 

 moment of inertia or bending rigidity of the section. Such cores possess 

 shear-transmitting properties but are rather weak in compression, partic- 

 ularly in the circumferential direction. 



The demands of hydrostatic pressure loading are such that in order 

 to exploit the sandwich concept for pressure hull construction, a core com- 

 prised of elements which are compression resistant as well as shear 

 resistant is sought. For this latter application, the membrane loads are 

 predominant, whereas in aerospace applications, the bending-type loads 



are of prime concern. With the thinking directed along these lines. Buhl 



72 

 and Pulos conducted a series of exploratory structural model tests to 



investigate the strength- weight advantages of sandwich-type cylindrical 



pressure hulls having "hard" cores. The configurations which have 



received the most attention include the web-type and tube-type core 



arrangements. The earlier results found by these investigators indicated 



that collapse -strength advantages on the order of 25 percent may exist 



over the conventional ring- stiffened cylinder in certain ranges of 



geometry; this is shown qualitatively to some extent in Figure 22. 



73 

 More recent experimental studies conducted at the Model Basin on 



sandwich cylinders have revealed another possible strength advantage 



inherent in these type hull structures. Hydrotests of some structural 



127 



