Utilizing such a simple polariscope the residual stresses were 

 investigated in both model and large-scale acrylic plastic capsules after 

 annealing was completed. Since the highest typical stresses in the joints 

 are found at the corners of the pentagons, all of the measurements for typical 

 residual stresses were performed at those locations. Using the photoelastic 

 stress investigation technique the highest typical residual shear stresses in the 

 acrylic plastic capsule models were found to be approximately 1 ,300 psi 

 (blue color) for solvent-bonded joints (blue. Figure 41) and 1,300 psi for 

 cast-in-place self-polymerizing PS-18 bonded joints (blue, Figure 44). In 

 the large-scale acrylic plastic capsule (Figure 54) the typical residual shear 

 stresses in the cast-in-place PS-18 adhesive joint were approximately 500 psi. 

 The magnitude of residual stresses around stress raisers in the joint is described 

 separately, as their magnitude depends more on the quality of bonding rather 

 than type of adhesive. 



The worst residual stress raisers were found to be in the cast-in-place 

 PS-18 joints at locations where either a trepanning operation was performed 

 to fill a cavity or interface separation with adhesive (Figure B-2), or where 

 one filling of the joint with adhesive terminated and another one was initiated 

 (Figure B-3). Small or large cavities (air bubbles) in the cast-in-place adhesive 

 joint did not act as residual stress raisers (Figure B-4). 



On the basis of the photoelastic investigations into the magnitude and 

 distribution of residual stresses in the bonded joints, several findings have 

 been made: 



1 . Using the magnitude of residual stresses at the tips of the pentagons 

 as a yardstick of comparison, there is very little difference in the effect that 

 the solvent or self-polymerizing adhesive has on the magnitude of typical 

 residual stresses in the joints if all the joints in the sphere are bonded in one 



or two increments. 



2. Joints in capsules bonded in numerous small increments with 

 self-polymerizing standard PS-18 adhesive have more stress raisers than joints 

 in capsules bonded simultaneously by the solvent or self-polymerizing adhe- 

 sive technique. 



3. The stress raisers in the joints filled incrementally by self-polymer- 

 izing adhesive are the result of incremental bonding process, where one 

 section of the joint hardens before the next one is filled with adhesive. 



4. Trepanning operations (drilling a hole to a cavity in the joint and 

 filling it with self-polymerizing adhesive) creates a serious residual stress 

 concentration. 



5. Cavities in the joint do not create significant residual stress 

 concentrations. 



178 



