800 



~ 700 



a 



600 



1 500 



1 400 



% 300 



8 



$ 200 



> 



1 100 



Notes: 



1. Pressurizatlon rate — 4. Sphere dimensions — 66-in. 

 16 psi/min OD x 61-in. ID 



2. Temperature — 65 to 68°F 5. Material — grade G Plexiglas 



3. Total Internal volume — 

 js 2,000 liters 



30 



40 



50 



Volume Displaced (liters) 



Figure 105. Change in displacement of 66-inch-diameter capsule under 

 short-term loading. 



2. The relaxation periods at zero pressure, which were chosen for all 

 pressure cycles to be equal in length or longer than the duration of sustained 

 pressure periods, appeared to be sufficiently long for all strains to return to 

 zero (Figure 107). Thus, the magnitude of strains in acrylic at the initiation 

 of each pressure cycle rose by the last cycle from zero to only 100 juin./in. 

 This took place regardless of whether the length of each cycle was 2, 15 or 

 60 minutes. 



Long-term strains were also recorded at 27 locations while the hull 

 was subjected to long-term loading of 24-hour duration at 100-, 200-, 300-, 

 400-, 500-, 600-, 700-, and 800-psi external hydrostatic pressure. Since the 

 relaxation periods were sufficiently long between each long-term pressurization 

 to allow for a complete relaxation of the hull, the recorded strain data was not 

 considered to be contaminated by viscoelastic strains still undergoing relaxa- 

 tion when the next pressure cycle was initiated. 



1. At room temperature, the magnitude of strains in the equatorial 

 region under long-term hydrostatic loading after a given duration of sustained 

 loading appears to vary linearly with pressure. To what maximum pressure 

 this relationship remains linear is not known, as the long-term pressure tests 

 were conducted only to 800 psi, at which pressure the relationship still con- 

 tinued to be linear (Figures 108, 109, 1 10). 



2. Upon depressurization, the strains in the equatorial region returned 

 almost to zero, even after long-term 800-psi pressure loading. This appears to 

 indicate that even at an 800-psi long-term hydrostatic loading in the 68 to 70°F 

 temperature range, the strains in the capsule (with possible exception of polar 

 regions) are probably still viscoelastic (Figures 109 and 1 10). 



141 



