Figure C-4. Typical birefringence in 

 photoelastic coating on 

 two-dimensional nnodel 

 of tie-rod head under a 

 3,000-pound tensile load. 



End-Closure Model 



The two-dimensional 

 model of the end closure and 

 end-closure flange when subjected 

 to simulated hydrostatic pressure 

 with the hydraulic loading jig 

 indicated that a serious stress 

 concentration does exist in the 

 meridional plane of the end 

 closure. The progress of the 

 photoelastic fringes across the 

 thickness of the model during 

 loading indicates that the local 

 stress concentration is caused 

 primarily by flexure of the end 

 closure at its flange. The magni- 

 tude of the stress concentration, 

 based on the average membrane 

 stress present in the model at 

 locations distant from the stress 

 raiser, is approximately 3.3 to 

 3.5. 



Segmented-Wall Model 



The testing of the segmented- 

 wall laminae fabricated from 

 photoelastically active epoxy 

 showed that as previously predicted a serious stress concentration is generated 

 by the presence of the stress raiser in the form of the shear pin holding the 

 segmented-wall laminae together. Since the fit of the pins in the holes and the 

 distance between holes in each individual segment laminae influence to a large 

 degree the magnitude of stress concentrations both in the pin and in the segment 

 laminae, the experimentally determined value of the stress concentration can 

 be considered only a representative value. The magnitude of tensile stress 

 concentration in the segment laminae around the shear-pin hole was found to 

 be approximately 3.5, while the compressive stress concentration caused by 

 the pin bearing against the edge of the hole was found to be approximately 

 6.5 in comparison to the nominal tensile stress in the narrowest cross section 

 of the segment. 



82 



