Two items of interest are apparent from the surface plots: (1 ) the 

 flexural bending behavior exhibited by the t/d = 0.25 viewports and the 

 absence of bending exhibited by the t/d ratios of 0.75, 1 .25, and 1 .75; and 

 (2) the absence of high effective stresses at the high-pressure face corner. 

 Generally speaking, this latter area appears to be in almost a hydrostatic 

 stress state which means that some structural modification could be made in 

 this region (refer to Appendix A). 



Displacements. Figure 14 illustrates the displacements at the center 

 of the low-pressure face. The results are presented in nondimensional form 

 for use with any diameter viewport. Generally speaking, the difference in 

 displacement between the fixed and free boundary condition is the gross 

 distance that the viewport moves. Thus, the 60° included angle viewport 

 displaces much more in the free case, which causes the higher effective stress 

 at the low-pressure face corner. The 90° and 120° viewports displace less 

 and thus, the effective stress is less. The transition to flexural behavior is 

 evident in Figure 14 by the knee in the curve at about t/d = 0.6. Two 

 additional points (t/d = 0.45) from the analysis in Appendix A are included 

 in Figures 14, 15, 16, and 17. 



Figure 14 is also used in the Design Recommendations section of the 

 report for calculating elevation of the viewport in the flange. 



Comparison of Experimental and Analytical Results 



Figures 15 and 16 provide a comparison of experimental and 

 analytical results. Figure 1 5 is based on the operating pressure and shows 

 an excellent comparison. The experimental data is based on post-test 

 observations of the six experimental viewports, while the analytical data is 

 based on the magnitude of the effective stress at the low-pressure face corner. 

 Cracks determined the presence of failure in the experimental viewports, 

 while the controlling factor in the analytical analysis was the pressure required 

 to equate effective stress with yield stress in the compression-compression- 

 compression octant. Note that the free boundary condition controls for the 

 range of the t/d ratios and that the analytical curves were shifted to the left 

 by 20% in accordance with the low temperature.^-''" Although the 35°F sea 

 water is on the high-pressure face, it is a fair assumption that the steel flange 

 has a low-temperature-gradient throughout and thus, provides a 35°F inter- 

 face with the viewport. 



16 



