EXPERIMENTAL PROCEDURE 



The objective of the experimental study was to generate a set of performance 

 curves that would serve as the basis for designing flat acrylic windows for use under 

 short-term hydrostatic pressure. Also the critical pressures for windows had to be 

 determined before further optical studies could be undertaken. Therefore, experi- 

 mental data not only had to cover the whole range of depths encountered in the 

 ocean, but also had to be applicable to flat windows of different thicknesses and 

 diameters. 



To meet these objectives, window test specimens had to be designed that 

 upon testing would provide the necessary data on which generalized window design 

 curves could be based. This was accomplished by selecting two nondimensional 

 parameters for dimensioning the windows. Use of the t/D| ratio and the Dq/D; ratio 

 (see "Terminology" and Figure 1) permitted not only the adequate description of any 

 window, but also scaling window dimensions up or down. In order to cover the whole 

 depth range in the ocean, the thickness component (t) of the \/D- ratio was varied 

 from 0.125 inch to 2 inches, while to prove the applicability of experimental data 

 to all possible window sizes the flange opening diameter (Dj) component of the ratio 

 was varied from 1.5 inches to 4.0 inches (Table 1). Flanges and some of the windows 

 are shown in Figures 2, 3, and 4. The flange seat diameter ratio (Dq/D;) was not 

 varied during the generation of the experimental data serving as basis for generalized 

 design curves because there were indications (see Appendix A) that varying this param- 

 eter would unduly complicate the study. For the same reason the various methods 

 for retaining the window in the flange were not investigated, although earlier explor- 

 atory experimental data shows^ that for some t/Dj and t/D^ ratios, the type of edge 

 restraint used on the window has a considerable influence on the critical pressure of 

 the window. To avoid confounding the data, the windows in this study were not 

 clamped or lapped in place, but simply sealed with grease Into the flange cavity with 

 approximately 0.005 to 0.010 Inch radial clearance between them and the flange. This 

 type of flat acrylic window mounting (shown In Figure 1) will be referred to In this 

 report as the DOL type III flange. 



Although in designing a flat acrylic window to be safe for underwater application 

 It is necessary to know the behavior of such windows under various types of hydrostatic 

 loading, only the short-term strength of windows was considered in this study. The 

 experimental evaluation of long-term and cyclic hydrostatic loading was relegated to 

 future studies on this subject. In the present study it is considered sufficient for design 

 purposes to have reliable data on only the magnitude of the displacement of the center 

 on the window's low-pressure face and the critical pressure at which a window of any 

 t/Dj ratio foils under short-term loading. 



