from overpressure to decrease to the level of strains generated by a simple 

 long-term loading at operational pressure varies with the duration of loading 

 at the overpressure level (Figure 112). 



100 150 



Time (minutes) 



Figure 111. Effect of temperature on viscoelastic strains on interior surface of 



equatorial region in 66-inch-diameter capsule under 500-psi sustained 

 hydrostatic loading. 



Long-term volume decrease, measured by the displacement of water 

 from the interior of the large-scale capsule, was performed only at three 

 different pressure loadings, as compared to nine different pressure loadings 

 for model capsules. From the volume decrease measurements performed on 

 large-scale capsule prototype, the following findings were made: 



1 . Long-term volume decrease is a function of both time and pressure. 

 However, for any given duration of loading, it is approximately linear with 

 the magnitude of pressure loading. The time-dependent rate of volume 

 decrease for any given pressure loading appears to decrease exponentially 

 with time, and to increase exponentially with the magnitude of pressure 

 loading (Figures 1 13 and 1 14). 



2. Upon depressurization from the long-term pressure loading, the 

 volume of the large-scale prototype capsule returned to its original size after 



a relaxation period of approximately the same duration as the long-term pres- 

 sure loading. The volume increase rates at the beginning of relaxation periods 

 were higher than the volume decrease rates at the beginning of the long-term 

 loading periods (Figure 1 15). 



146 



