Figure 51. Typical cavities in an imperfectly bonded segment of a joint in 

 66-inch-diameter capsule. 



After completion of bonding, the large-scale acrylic plastic hull was 

 annealed for 124 hours at 160°F in a temperature-controlled oven. The 

 annealing process did not remove all the residual stresses from the joints 

 resulting from the bonding process. The residual stresses in the joints were 

 found to be approximately of the same order of magnitude (but somewhat 

 less) as the residual stresses in the model capsule (Figure 54). The basic 

 difference between the residual stresses in the model capsule and the large- 

 scale capsule was in distribution. In the model capsule, the stresses are fairly 

 uniform in all of the joints, but in the large-scale capsule the magnitude of 

 stresses varies markedly from one location to another in the joint. This, of 

 course, is the result of bonding the joints in the large-scale capsule in small 

 increments, each solidifying before the next one is cast. Thus, it appears 

 that casting of joints in small increments is less desirable than casting them 

 in one or two increments, or preferably in a single operation. 



Polishing of the exterior and interior of the hull completed the 

 fabrication of the large-scale acrylic plastic hull. Sphericity and diametral 

 measurements revealed that zealous polishing of rough joints removed an 

 excessive amount of acrylic plastic. The lesson that could be drawn from 

 this is that polishing should be performed with great care, and if the choice 



