Considerable cold-flow crotering occurred on the high-pressure face before 

 the critical pressure was reached (Figure B-13). Both elastic and plastic extrusion on 

 the low-pressure face were also experienced by the window at this time (Figure B-14). 



Windows whose t/Dj ratios exceeded about 0.50 failed predominately by shear; 

 the conical fracture surface was unable to penetrate the thickness of the material 

 (Figures B-15 and B-16). At the critical pressure, the entire window was penetrated 

 by discontinuous cracks and the central portion (bounded by Dj) was completely 

 ejected. 



RESULTS OF TESTS 

 1.5-Inch (D|) Windows 



The 1.5-Inch (Dj) windows were tested In groups of five; the nominal t/D[ 

 ratios included the range from 0.083 to 0.667. For each group, critical pressure 

 was plotted against the t/Dj ratio (Figure B-17) and pressure was plotted against 

 the window's central displacement. 



The windows having t/D| ratios less than 0.2 exhibited both flexural and 

 conical failures. Parametric considerations were the window's radial clearance, 

 pressurlzatlon rate, and grease-seal thickness. No attempt was made to Isolate 

 these effects in this study. 



For a t/Dj ratio between 0.2 and 0.4 the principal failure was conical, the 

 cone's apex reaching the high-pressure face toward the upper limit of critical 

 pressure (Figure B-12). Audible cracking during pressurlzatlon occurred mostly at 

 levels above 75% of critical pressure and occurred fairly consistently between 90% 

 of critical pressure and failure. 



Windows of t/D; ratios greater than 0.4 failed predominantly by shear, 

 fragmentation being so complete that sometimes none of the window material was 

 retained In the flange. Extrusion of these windows caused audible cracking to 

 occur many times before critical pressure was reached. For t/Dj ratios of less than 

 about 0.25 pressurlzatlon to approximately 70% of critical pressure resulted in no 

 visible evidence (to the naked eye) that the windows had been pressurized. For 

 t/Dj ratios between 0.25 and 0.55, the extrusion of the window at 70% of critical 

 pressure caused a shallow Impression of the flange seat to appear (Table B-1); however, 

 on examination after release of pressure no visible Impairment of optical quality 

 Inside this Impression was apparent to the naked eye. For windows of t/Dj ratios 

 greater than 0.55, the development of cracks accompanied extrusion and depression. 



Details of flanges used in testing the 1.5-inch (Dj) windows are shown In 

 Figure B-18 and an in-place schematic Is shown In Figure B-19. 



34 



