For the performance of all the hydrostatic pressure tests, a special 

 cagelike holding jig was designed and fabricated for NEMO. Its purpose was 

 to protect the hull against impact when the capsule was placed into the 

 vessel and to act both as an anchor and as a support for the either positively 

 or negatively buoyant hull (depending on whether its interior was dry or 

 filled with water). When the interior of the hull was dry, it exerted approx- 

 imately 4,000 pounds of positive buoyancy force on the bottom plate 

 anchored to the holding jig. 



Although all the tests planned for the large-scale capsule were 

 basically of cyclic nature, the objectives of these tests varied from one 

 series of tests to another. In order to clarify these objectives, each series 

 of tests will be discussed below in detail. 



Time dependent strain under sustained pressure loading was to be 

 determined by pressurizing the hull to the desired pressure level and holding 

 it at that pressure until the time-dependent rate of strain increase stabilized 

 itself for that pressure. Since the time-dependent strain rate varies from one 

 sustained pressure level to another, the hull had to be held at different sus- 

 tained pressures for a sufficient time to establish the strain rates. The test 

 procedure established for this series of tests consisted of pressurizing the 

 hull to 100-, 200-, 300-, 400-, 500-, 600-, 700-, and 800-psi pressure levels 

 and holding it at each one of those levels for at least 24 hours. At the con- 

 clusion of every sustained pressure test, the pressure was decreased to psi, 

 so that the hull could relax between pressurization cycles. The relaxation 

 periods varied from 45 to 188 hours. For this series of tests, the interior of 

 the hull was dry and vented to the atmosphere. The ambient temperatures 

 of the hull interior and exterior were maintained in the 68 to 72°F temper- 

 ature range. 



The effect of cycling on the magnitude of strains in the hull was to 

 be investigated by pressurizing the hull to 500 psi, holding it at that pressure 

 for a period of time, depressurizing it to psi and holding it at that pressure 

 for the same length of time as at maximum pressure. Since the relaxation 

 period at psi was not necessarily always sufficient to permit complete 

 relaxation of the hull, some residual compressive strain would remain in 

 the hull at the beginning of the new pressure cycle and would influence 

 the strain during the succeeding pressurization cycle. By varying the length 

 of dwell time at the 500-psi level in each cycle, the magnitude of residual 

 strain in the hull was expected to vary from one series of cycles to another. 

 By comparing the strain rates in the hull generated during long and short 

 cycles, some indication of the effect of residual strains on the strain rates 

 could be obtained. To vary the dwell time as much as possible, the dwell 

 time at 500 psi was varied from 360 minutes to 2 minutes. For this series 



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