level in the metallic plate. If the stresses in the hatch plate of chosen dimensions 

 were found to be too high, an alloy with higher material properties could be sub- 

 stituted for the material originally chosen. This would result in no changes in 

 hatch design, while increasing thickness of the acrylic plastic hull would require 

 considerable redesign. 



To calculate the minimum thickness of the metallic plates, the assump- 

 tion was made that the metal plate is unaffected by the presence of the acrylic 

 plastic hull bearing upon it. Therefore the stress in the plate could be approx- 

 imated on the basis of membrane shell theory. Using a design stress of 13,500 

 psi (approximately 50% of minimum yield stress in type 316 stainless steel) 

 and the thin shell membrane shell equation 



P . ili i7i 



a hatch thickness of t/R = 0.0166 was calculated for p = 450 psi. When the 

 calculated hatch plate thickness was subsequently checked for its elastic sta- 

 bility with Equation 4, it was found to be elastically stable at operational 

 depth. Its failure was predicted on the basis of Equation 4 to take place by 

 plastic instability at pressures slightly in excess of 1,350 psi. Thus from the 

 viewpoint of instability failure, the design would appear to be adequate as it 

 would cause the hatch to fail at approximately the same depth as the rest of 

 the acrylic plastic sphere. To forestall generation of excessive stress raisers 

 around penetrations in the bottom metal plate, they were either reinforced 

 by local thickening of the plate in the form of bosses or flanges, or they 

 were subsequently filled by penetrators of approximately the same rigidity 

 as the plate. Detailed stress analysis of the metal plates was not performed 

 at that time as it was felt there was not sufficient information on the inter- 

 action between steel plate and acrylic plastic hull deforming viscoelastically 

 or viscoplastically to make the analytical stress analysis more than a first 

 order approximation. 



Structural Component Dimensioning. This constituted the last step 

 in the detail design of the acrylic plastic capsule. Before the detail design of 

 the structural components could be initiated, a procedural question had to 

 be resolved: Which acrylic plastic sphere size would be ultimately selected 

 for the capsule program? Although some capsule dimensions have been 

 calculated in nondimensional terms like t/R , and therefore apply to any 

 size sphere, most dimensions of the capsule details must be based on dimen- 

 sional human factors criteria (size of hatch, hatch locking mechanism, and 

 others). Thus, once the decision was made to design a certain diameter 

 capsule, a considerable waste of engineering and design time would occur 

 if the diameter of the capsule was changed. 



34 



