The above format explicitly sets forth the procedure used to determine the 

 capacity of the various viewport geometries. 



A further point of concern was in specifying the boundary condition 

 between the viewport and the flange. In order to account for all practical 

 contingencies, two extreme boundary conditions were applied to each view- 

 port configuration as shown in Figure 3: (1 ) the boundary was fixed, repre- 

 senting maximum friction between the acrylic viewport and its flange; and 

 (2) the boundary was allowed to be frictionless, representing perfectly 

 smooth, greased interfacing. Of these two boundary conditions, the one 

 resulting in the controlling failure as outlined above, was chosen as the 

 governing boundary condition. 



A structural response discovered during the course of the analysis 

 was that an arbitrarily high stress concentration existed in the element at the 

 corner of the low-pressure face for all viewport configurations and boundary 

 conditions. This phenomenon correlated with experimental findings where 

 it was discovered that the low-pressure face corner underwent deformation 

 or "rounding" for even the smallest load magnitudes (see Figure 4). 



An intensive analytical investigation, outlined in Appendix C, revealed 

 that the spiked stress concentration was relieved by deforming the corner of 

 the mathematical model as was suggested by the experimental models. Thus, 

 the viewport geometries considered in this report were all analyzed with a 

 predeformed corner characterizing an actual viewport after its initial loading. 



The last analytical refinement considered was to investigate the 

 response from an 0-ring groove machined in the acrylic. The analytical 

 results along with the experimental tests are presented in Appendix A. 



Input to Wilson's code^ required material properties for acrylic. 

 Reference 5 describes experimental tests performed to determine these 

 necessary values at room temperature as: modulus of elasticity, 444,000 psi; 

 and Poisson's ratio, 0.4. 



RESULTS AND DISCUSSION 



Experimental 



Post-test visual observations and displacements at the center of the 

 viewport low-pressure face served as experimental data. Since the viewports 

 were all exposed to the same pressure loading and environment, the cause 

 of any post-test effects would be the differences in structural design (all 

 other variables considered equal). 



