4. In the actual viewport, a sharply spiked stress concentration exists at the 

 low-pressure face corner which results in rounding of the sharp corner. 



5. The transition to the dominance of flexural bending behavior occurs at 

 about t/d = 0.6. 



6. The stress distribution for conical frustums is independent of elastic 

 modulus and only slightly dependent on Poisson's ratio, thus, the structural 

 design curves are generally applicable to materials other than acrylic. 



7. A conventional 0-ring design with the groove located in the viewport 

 conical face satisfactorily fulfills the requirements for viewport sealing 

 (Appendix A). 



DESIGN RECOMMENDATIONS 



The purpose of this section is to provide the designer with the 

 necessary information to design a vehicle viewport accurately, quickly, and 

 safely. The type of analysis used in this section was experimentally verified 

 as previously described. 



In order to design a conical acrylic vehicle viewport, the designer 

 must have available such information as: t/d ratio, included angle, elevation 

 of viewport in flange, method of sealing, and flange surface finish. The 

 design requirements would, of course, include the operating pressure, ambient 

 temperature, and maximum length of dive. 



This section of the report deals with design curves for viewport 

 dimensions and recommendations for elevation of viewport in flange. Design 

 recommendations for the flange surface finish are in Reference 5, and an 

 analysis of the viewport sealing problem is in Appendix A of this report. 

 Annealing instructions for the viewport may be found in Appendix B or 

 Reference 1 1 . 



Design Curves 



Material. Figure 18 represents the material facet of the design or 

 the relationship between the yield stress of acrylic and time. A more detailed 

 discussion of the origin of these curves is presented in Appendix C. The 

 figure contains both tensile and compressive curves. The yield strengths can 

 be seen to reduce to about 50% of the instantaneous value after 500 hours. 



27 



