





















: XI to 34°F 

















50 to 70°F 













98 



to 102°F 























1. Pres 



surization rate— 100 psi/min 









2. Dimensions of Ihe spheres — 









15-in.ODx 14-tnJD 











erial — grade G Plexiglas — 

















4. NEMO at O-psi pressure 









displaces 28.5 liters of water 



1 1 1 



400 

 Volui 



600 800 1,000 1,200 1,400 

 ie Decrease (ml) 



Figure 79. Change in displacement of acrylic 

 plastic capsule models as a function 

 of hydrostatic pressure under short- 

 term loading. 



8. All strains measured on 

 the interior or exterior surfaces of 

 the acrylic plastic hull were com- 

 pressive. The meridional and hoop 

 strains on the capsule models mea- 

 sured at their equator were of 

 approximately the same magnitude. 

 Their relationship to the hydro- 

 static pressure under short-term 

 loading was linear to at least a 

 750-psi loading (Figure 81). The 

 strains in the immediate vicinity 

 of the steel end plates differed 

 from those measured at the 

 equator. This was indicated both 

 by the magnitudes of strains mea- 

 sured there with electric resistance 

 strain gages and by photoelastic 

 techniques. From these readings, 

 it appears that the maximum stress 

 encountered around the steel end 

 plate is at the very edge of pene- 

 tration on the interior surface of 

 the sphere. The meridional stress 



is in the elastic range of acrylic approximately 8 to 10 times higher than the 

 stress measured at the equator at the same pressure (Figure 82). The circum- 

 ferential stresses at the same location are, on the other hand, only 2 to 3 

 times higher than those found at the equator (Figure 83). In general, the 

 distribution of stresses near polar penetrations indicates that bending 

 moments are superimposed upon the membrane stresses in the vicinity of 

 penetration through the acrylic plastic hull. Also, since at the 500-psi 

 pressure the stress at the equator is in the 3,000-to-4,000-psi range, plastic 

 redistribution of stresses probably takes place in the acrylic plastic at the 

 edge of penetration. 



Long-term tests performed on 13 model capsules over a period of 

 3 years (Table 5) at room temperature have shown that long-term sustained 

 pressure loading is a very important test condition for acrylic plastic pressure 

 hulls, as this test condition causes the acrylic plastic pressure hulls to fail in 

 a mode that is not detectable by short-term tests. The major findings resulting 

 from the long-term sustained hydrostatic tests of NEMO models are: 



19 



