One of the requirements which the joint must satisfy is an ability to 

 withstand large bending moments to which Benthos will be subjected when 

 launched on ASW missions from deck-mounted air-operated tube launchers. 

 For this reason, a prototype model of the joint was built and tested to 

 destruction under bending moments. Since alloys used in the production 

 version of the joint were not available at that time, the prototype joint 

 was built from 7075-T6 aluminum alloy. For the flexure tests, the joint 

 was mounted to steel cylinders with end flanges identical to those in the 

 ceramic Benthos shells. Under a two-point flexure test (Figure 28), the 

 joint failed at 170,000 pound inches of bending moment by shearing of 

 threads in the breech- lock at the point of highest tensile stress. When 

 the test data obtained from testing the 7075-T6 aluminum joint is extra- 

 polated to 7001-T6 aluminum and Tl- 6Al-6V-2Sn titanium alloy joints, 

 their fracture strengths are predicted to be 220,000 and 340,000 pound 

 inches, respectively. Since these bending moments are in all probability 

 larger than moments required to fracture the ceramic shell sections, the 

 strength of the metallic joints to withstand bending moments is considered 

 more than adequate. 



During the fabrication of the shell sections, the highest possible 

 quality control was exercised. Unlike any other ceramic material, Pyro- 

 ceram ceramics are transparent in the initial stages of fabrication, and 

 visual inspection methods are used to examine them for internal defects 

 (Figure 30) . Optical glass-melting techniques are used to assure uniform 

 composition, constant density, freedom from bubbles and striations, and 

 uniform electrical properties. Subsequent controlled heat-treating cycles 

 activate special nucleating agents in the body to produce a fine-grained, 

 uniform crystal growth. No problems have been encountered in the ceraming 

 of the thick- walled cylindrical, hemispherical, and conical blanks from 

 which subsequently excess material is removed by grinding. Using a tracer 

 lathe and proper guide templates, the excess material is removed until a 

 rib- stiffened structure with integral ribs results (Figure 29). The grin- 

 ding operation lends itself to very close dimensional tolerance control; 

 the final product of the fabrication is within + .010 inch of specified 

 nominal dimensions. 



Summarizing, it can be stated that Benthos is an antithesis to DIVEAR. 

 Whereas the latter downrates design stresses in glass for the sake of 

 economy in fabrication, the former demands and obtains reliable design 

 stresses in the ceramic hull unattainable by the employment of any other 

 commercially available material, except possibly 99-percent alumina ceramic. 

 In Benthos, ceramics do not have to justify their application on a basis 

 of cost in competition with other materials, but on the basis of being the 

 peer without rivals among high- strength structural materials. No other 

 material can provide Benthos with its unmatched deep submergence design 



300 



