Short-term strength of the large-scale acrylic plastic capsule was 

 determined by pressurizing it externally to implosion at a 100 psi/min rate 

 with water at 70°F ambient temperature. The implosion took place at 

 1,850 psi with a failure mechanism similar, if not identical, to that of the 

 models previously imploded under short-term loading. From the observa- 

 tion of the fragments from the imploded sphere as well as comparison of 

 the failure pressure of the large capsule and model capsules the following 

 findings were made: 



1 . There appears to be no material mass scaling effect, common to 

 glass or concrete structures, in acrylic plastic since the 1,850-psi implosion 

 pressure of the 66-inch capsule matches closely the 1,827-psi pressure pre- 

 dicted for the large-scale capsule on the basis of model capsule tests. This 

 prediction is based on the 1,575-psi average implosion pressure of the 

 15-inch acrylic plastic models and the fact that the minimum wall thickness 

 of the 66-inch capsule is 16% greater than the minimum thickness of the 

 models. 



2. The fragmentation of the large-scale capsule was similar to that 

 of models (Figure 116). In most cases, the fracture planes cross the joint 

 bonds indicating that the joints did not serve as planes of weakness. 



Figure 1 1 6. Overview of the structural fragments from the imploded 66-inch-diameter 



capsule. Note that the acrylic plastic fragments are not rectilinear, indicating 

 that fracture did not take place along the bonded joints. 



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