Figure 23. Failed end closure from 

 the stacked-ring pressure 

 vessel. Note the circum- 

 ferential fracture which 

 caused the end closure 

 to separate from its flange. 



split shear nut 



split nut keeper 

 retaining flange 



stacked rings 



Note: All structural components 

 are of acrylic plastic except 

 the aluminum end closure 

 and split nut keepers. 



Figure 24. Test arrangement for 

 hydrostatically testing 

 tie rods to failure. 



2. Principal stresses of almost the 

 same magnitude as on the hemi- 

 spherical end closures were measured 

 on the tie rods in axial directions. 

 Since rosettes 12 and 13 were located 

 away from the rod heads, the stresses 

 indicated by them represent the 

 average stress in the tie rods (Figures 

 35 and 36). 



3. The principal stresses on stacked 

 rings in the hoop direction were 

 next in magnitude. The absence of 

 tensile stress in the axial direction 

 indicated that the stacked ring, as 

 postulated, did resist only radial 

 forces exerted by the internal hydro- 

 static pressure in the vessel (Figures 

 37 and 38). 



4. The principal stresses on the 

 monolithic end-closure retaining 

 ring were the least in magnitude, 

 indicating that unless the magnitude 

 of stress raisers at the root of the 

 flange instep was high, the failure 

 of the vessel would probably not 



be initiated in this structural compo- 

 nent of the vessel (Figures 39 

 through 43). 



5. Fracture of the structural compo- 

 nents generally took place either in 

 locations where stress raisers were 

 either known or surmised to exist 

 (Appendix C). Thus, it was surmised 

 prior to the destructive testing that 

 the failure of the hemisphere would 

 take place in equatorial plane some- 

 what above the flange on the 

 hemispherical end closure. The 

 failure that did take place there was 



30 



