the finished product represents a fairly homogeneous glass mass of sur- 

 prisingly good quality when one considers the 215-pound monolithic mass 

 of glass involved in the structure. 



The ends of the hull were capped with 7075-T6 aluminum hemispheres 

 machined to accept internal and external attachments plus several feed- 

 throughs (Figure 17) . The bearing area between the end caps and the glass 

 cylinder is a generous one and relies on t he flatness of the aluminum and 

 glass flanges for elimination of point loadings. Sealing is accomplished 

 with an 0-ring located in an 0-ring groove in the aluminum flange under 

 axial compression. 



In general, the DIVEAR structure has the minimum of structural refine- 

 ments necessary to withstand the operational depth of 20,000 feet. Further- 

 more, to keep the cost down to an absolute minimum, extremely generous 

 dimensional tolerances are permitted which vary from + 1/8 to + 3/8, 

 depending on the dimension described. Thus, to insure the integrity of 

 the glass cylinder at the operational depth, even with stress concentra- 

 tions produced by the eccentricity and variation in thickness of the 

 cylinder and stiffeners, maximum design stress for the nominal dimensions 

 of the cylinder is only 87,000 psi, definitely a low stress level for glass 

 but still considerably higher than the stress experienced by current 

 models-'--'- of spherical submarine hulls tested to 20,000 feet. Still, this 

 design stress surpasses the operational stress level that could be safely 

 specified for any commercial high- strength aluminum, glass fiber epoxy 

 laminate, or HY80 steel. Only the more expensive high-strength titanium 

 alloys or steels could carry such design stress safely, and then only if 

 the dimensional tolerances were appreciably tighter than those specified 

 for DIVEAR. The cost of the DIVEAR structure then, if fabricated from 

 any other material that would give it the same weight (aluminum end clo- 

 sures included) to displacement ratio of .65 at 20,000 feet, would be 

 higher than incurred in fabrication of Pyrex DIVEAR. The cost of this 

 280-pound aluminum- capped Pyrex hull is approximately $35 per pound of 

 payload- carrying buoyancy. Thus, although in this particular design the 

 design stresses have been set low to capitalize on the cost savings 

 afforded by the loose dimensional tolerances of the glass hand-blowing 

 process, the structure is still competitive in cost with similar structures 

 fabricated from the commercially available maraging steel and titanium 

 alloys which give the structure the same weight to displacement ratio and 

 20,000-foot depth capability. If Pyrex DIVEAR hull performs in hydro- 

 static proof tests as predicted, then this approach to fabrication of 

 inexpensive glass instrumentation capsules is justified. It is worthwhile 

 to note here, however, that by discounting the mechanical strength of glass 

 to meet the loose tolerances of the more economical fabrication method, the 

 DIVEAR glass hull has been placed in a weight to displacement ratio cate- 

 gory where the major justification for the use of glass as the structural 



286 



