3. All of the steel end closure components except for the top hatch 

 ring and associated split retaining rings showed extensive plastic deformation 

 (Figure 117) indicating that the large-scale polar steel closures underwent 

 plastic buckling at approximately the same pressure as the model scale steel 

 closures which failed at 1,800 psi (Figure 80). This validates the linear scaling 

 factor (diameter of prototype capsule/diameter of model capsule) used in the 

 scaling up of model capsule end plates for use in the 66-inch prototype NEMO 

 capsule. 



Figure 117. Steel polar closure assemblies from the imploded 

 66-inch-diameter capsule. 



4. The general implosion of the prototype NEMO capsule was triggered 

 by the plastic buckling of the bottom plate. This finding is supported by the 

 fact that (a) only on the bottom plate were the hatch retaining rings twisted, 

 (b) only on the bottom plate was the spherical beveled bearing surface severely 

 distorted, (c) only the bottom polar pentagon had its beveled bearing surface 

 severely damaged (Figures 1 18 and 1 19), (d) rosette 3 mounted at the location 

 where plastic hinge in the bottom plate formed showed the highest stress level 

 during previous tests to 500 psi. 



5. Since the buckling of the hatch and of the bottom plate was plastic 

 rather than elastic, it can be avoided at pressures less than 2,000 psi by sub- 

 stituting material with a yield point above 60,000 psi for the type 316 stainless 

 steel used in the prototype. 



150 



