1 



relaxation 









800 psi 



at psi 





c^ 





700 psi 











600 psi 

 500 psi 



Motes: 



1. Pressurization rate — 50 psi/min 



2. Temperature — 68 to 70°F 



3. Dimensions of sphere — 

 66-in. OD x 61-in. ID 



4. Material — grade G Plexiglas 







400 psi 

 300 psi 



" 

















200 psi 

 100 psi 











12 3 



3 

 Time (minutes x 10 ) 



Figure 1 10. Typical viscoelastic strain on interior surface of equatorial region 



in the 66-inch-diameter capsule under sustained hydrostatic loadings 

 of different magnitude and subsequent relaxation. 



5. The strain, as well as the time-dependent strain rate, vary with the 

 temperature of the pressurizing medium. Comparison of strains and strain 

 rates in 32 to 35°F temperature range with those in the 68 to 70°F range 

 shows that in the low temperature range they are smaller by about 20% to 

 30% (Figure 111). 



6. If the acrylic plastic capsule is depressurized to some pressure level 

 above psi, the strains will initially begin to relax as they do when the external 

 pressure level is reduced to psi. After a period of time, the time-dependent 

 relaxation of strains will cease and time-dependent increase in strain will begin, 

 but the rate will be lower than for hulls not previously loaded to higher pres- 

 sure levels. However, after a sufficiently long period of time, the strains reach 

 the same equilibrium point regardless of whether the hull was first loaded to 

 some overpressure and then depressurized to the operational pressure level or 

 the pressure was raised to the desired level directly from psi. Upon depres- 

 surization to operational pressure, the time required for the strains resulting 



145 



