Analytical Phase 



The viewport was simulated using the finite element method to obtain 

 effective stress values at critical points for later analysis. The mesh contained 

 664 nodal points and 610 elements. Both the free and fixed boundary con- 

 ditions were used in this analysis. 



RESULTS 



Experimental 



The viewport with theO-ring was loaded at 4,000 psi for a total time 

 of 200 days before the creep leveled off. Post-test observations, as shown 

 in Figure A-3, indicated rounding of the corner and presence of cracks. 

 Inspection of theO-ring groove, however, found no crazing or cracks whatso- 

 ever. Figure A-4 presents the absolute displacement at the center of the 

 low-pressure face versus time in days. Creep accounted for 35% of the total 

 displacement at 200 days. Even with this much displacement theO-ring 

 did seal when the dive was completed and the viewport was relaxing. 



4,000 psi 





65° to 75° 



F 







-—- ^ 









f 





















50 psi/min 

















t/d= 



a = 9 



.45 

 0° 









d =8.4 in. 

 h =0.21 in. 



120 



160 



Time, T (days) 

 Figure A-4. Displacement response of viewport with recomnnended seal design. 



38 



