one actually used in the acrylic pressure vessel. After fabrication of the 

 cross-sectional metallic models of different tie-rod heads, they were coated 

 with photoelastic epoxy and subjected to tensile load tests (Figures C-2 

 through C-4) in a standard tensile load machine. The machine utilized a 

 specially designed load applicator and the distribution of photoelastic fringes 

 was recorded. Since the strains in the tie rods of the pressure vessel are uni- 

 axial, it was felt that testing models (representing their longitudinal cross 

 section and subjected to axial tensile loads) would adequately simulate the 

 loading in the full-sized structural part. 



For the investigation of strains in the closure flange, a metallic cross- 

 sectional model was made. Since the flanges on the closures are subjected to 

 three-dimensional strains when the interior of the vessel is pressurized, it is 

 impossible to measure all of their triaxial components with simple biaxial 

 cross-sectional models. However, it is known which load components generate 

 the largest concentration of strains in the closure flange. Thus, cross-sectional 

 models can be designed to show under biaxial loading the largest strain concen- 

 trations present in the actual closure flange. 



To measure the strains in the meridional plane of the flange caused by 

 both the shear, membrane, and flexural stresses in the closure under hydrostatic 

 loading, a cross-sectional model was made that represented the cross section in 

 the axial plane of the whole vessel closure (Figures C-5 and C-6). To load this 

 cross-sectional model of the closure to simulate the hydrostatic loading imposed 

 on the end closure by the fluid inside the pressure vessel, a hydrostatic loading 

 jig was devised. This jig, utilizing hydraulic pressure acting on a laterally con- 

 strained 0-ring mounted in a plate contoured to the internal radius of the 

 vessel's hemispherical closure, simulated very effectively the hydrostatic loading 

 acting on the actual vessel closure. The closure cross-sectional model was coated 

 with epoxy prior to investigation under polarized light, since it was made of 

 metal. During the application of simulated hydrostatic pressure with the hydrau- 

 lic load application jig, photographs were taken of the photoelastic fringes at 

 50-psi intervals (Figure C-7). It is to be understood, however, that although 

 the cross-sectional model gave a good representation of strains and strain con- 

 centrations in the closure adjacent to the flange caused by shear, flexure, and 

 axial stresses in it, the model did not help in the determination of strain concen- 

 trations caused by hoop stresses in the flange and in the closure wall adjacent 

 to it. These strain concentrations are caused by the abrupt change in the cross 

 section of the closure wall. Since determination of the magnitude of this strain 

 concentration would involve the use of a three-dimensional model for frozen 

 photoelastic strain technique, this investigation was omitted. It was felt, however, 

 that the strain concentrations caused by the shear, axial, and flexural stresses in 

 meridional plane are much more severe than the one caused by hoop stresses. 



78 



