pR 



pressure of 10, 000 psi, according to the simple relation cr = — , in an 



y h • 



unstiffened cylinder of the same outside diameter as the prototype. The 

 shell thickness was then calculated in a like manner for an unstiffened 

 cylinder of the same diameter as a "model" of structural design similar 

 to that intended for the prototype and subjected to a pressure equal to the 

 collapse pressure realized from tests of that "model." The "model" 

 chosen as a datum was Model SP-3, a web-stiffened sandwich cylinder, 

 the results of which are presented in Reference 2. With this latter value 

 of shell thickness, the weight per unit of displaced volume ■was determined 

 for the unstiffened cylinder. Then the shell thickness calculated for the 

 unstiffened cylinder, based on the proposed prototype requirements, was 

 reduced by the ratio of the unit weight of Model SP-3 to that of the equiv- 

 alent unstiffened cylinder. This reduced thickness for the proposed pro- 

 totype was then distributed in the form of a web- stiffened sandwich cross 

 section having the same weight per unit length. For convenience, the two 

 coaxial cylindrical shells and the web stiffeners were specified as having 

 the same thickness; however, subsequent calculations have shown that 

 this need not represent optimum distribution of the material. 



The first model tested (Model OV-1) was fabricated of high strength 

 steel and was intended primarily to determine the interbay strength of the 

 typical sandwich section and to verify the axisymmetric elastic behavior 

 predicted by the analysis of Reference 3. Also, the long lead time and 

 great cost required to obtain the necessary titanium material and the lack 

 of well-defined fabrication procedures to build a welded titanium model 

 within a short time necessitated the use of an equivalent- strength steel 

 to check the basic design. 



The dimiensions and design details of Model OV-1 are shown in Fig- 

 ure 3. These dimensions were dictated by the size of high-pressure test 

 facilities then existing at the Model Basin and by the availability of suit- 

 able thickness material on hand. The entire model was fabricated from 

 a single steel plate having an average thickness of 0.242 in. and heat- 

 treated to a compressive yield strength of approximately 115, 000 psi. The 

 yield strength of the shell material ranged from a low of about 109, 000 to 

 a high of about 117, 000 psi. Yield strength values of 114, 000 and 111, 000 



