proper design ratio between the window thickness and the unsupported 
diameter of the window. Because acrylic plastic plate stock varies in 
thickness from specified values, the actual t/D, ratio of finished 
windows varies from the specified one (Figure 1). Since previous tests 
have shown that a 1.5 ratio between the flange opening and the outer 
window diameters is desirable the existing EDU window flanges (Figure 2) 
were checked for conformance. They were found to conform approximately 
to this ratio. It was found, however, that modification of the existing 
retaining ring (Figure 3) for the EDU chamber flange with the 7.000-inch 
diameter seat was required to accommodate the 1.650-inch thick acrylic 
plastic window. No further changes in the EDU window flanges were found 
to be necessary to accommodate the acrylic plastic windows chosen on the 
basis of 0.325 t/D. ratio. The sealing arrangement consisting of flat 
rubber gaskets used previously with glass windows was retained unchanged 
for acrylic plastic windows. 
Material Selection 
Since the utility grade of acrylic plastic Plexiglas G (MIL-P-21105C) 
has been found in previous studies to be acceptable for man-rated windows 
under hydrostatic loading, it could be utilized for EDU windows without 
any further material selection tests. But if the fabricator of windows 
would rather supply an equivalent or better grade of acrylic plastic for 
the windows, it could be utilized also, providing the typical window 
performance evaluation tests were performed with windows fabricated from 
that material. 
Because Swedlow Inc., the fabricator of the windows, indicated that 
he would rather use Swedlow 350 grade (MIL-P-8184) acrylic plastic, it 
was chosen for the EDU windows. The advertised mechanical properties of 
Swedlow 350 acrylic were approximately the same as of Plexiglas G acrylic. 
Therefore, no fear existed that it may not pass the NCEL specifications 
(Table 1) for man-rated acrylic plastic windows. The basic difference 
between Swedlow 350 and Plexiglas G was in the former's better resistance 
to (1) surface crazing when exposed to harmful chemicals, and (2) defor- 
mation at elevated temperatures. Since this difference between Swedlow 
350 and Plexiglas G was to EDU's advantage, it was accepted as a desirable 
feature. 
Material Quality Control 
Material quality control was exercised by cutting test specimens 
from the center of the acrylic plastic plates serving as machining stock 
for the windows. Since the existing specification MIL-P-8184 covered 
the optical and physical properties of the Swedlow 350 material no need 
existed to repeat these tests on the plate in stock. Thus, only mechani- 
cal properties tests were run on the material test specimens cut from 
each acrylic plastic plate used as stock for machining of the windows. 
If the tests showed that the mechanical properties were lower than speci- 
fied, the acrylic plastic plates from which the test specimens were taken 
