subjected during its life as a part of the NEMO system. Some of the models 

 (Table 5) were equipped with operational end plates while others had the 

 simulated polar plates. Model 1 with operational polar plates was without 

 tie rods. All models with simulated polar plates were pretensioned by means 

 of the rods. The operational end plates were connected by means of four tie 

 rods (Figure 57), and the simulated polar plates were connected by a single 

 tie rod (Figure 64). 



Two of the model capsules (2 and 1 1 ) were subjected to cyclic 

 pressurization (Table 6) before being tested to destruction in the long-term 

 tests. Because of their previous test history, a somewhat lower performance 

 level during the long-term tests could be expected, and if it actually occurred, 

 could be accounted for. 



Cyclic tests were performed on four models (Table 6). The reason for 

 choosing such a low number of models for cyclic tests was not a lack of appre- 

 ciation for these tests but a lack of appropriate controls on the pumping 

 system available for performance of cyclic pressurization tests. Different 

 durations of cycles were selected for testing each model (Table 6). This 

 decision was based on the rationale that since the effect of cycle duration 

 on the cyclic life of an acrylic plastic pressure hull is unknown, cyclic tests 

 with different durations must be utilized to cover the range of cycle profiles 

 to which the NEMO system may be exposed during actual operation. 



Pressurization and depressurization were both accomplished at a 

 100-psi/min rate by pneumatically powered positive displacement pumps. 

 The temperature of the water during the performance of the cyclic tests 

 was that of the ambient atmosphere, and therefore, as in the long-term tests, 

 the temperature of the water varied from day to day within the 50 to 80°F 

 range. The variations in ambient temperature were accompanied by variations 

 in pressure as the water in the pressure vessel expanded or contracted with 

 temperature. The variation in maximum pressure was particularly pronounced 

 for the cyclic tests with long dwell time at the maximum pressure. The pres- 

 sure, however, never exceeded 550 psi or went below 400 psi during dwell 

 time at the nominal maximum pressure of 500 psi. 



All the capsule models subjected to cyclic loading had no previous 

 pressurization history except for Model 2, which had previously undergone 

 two cyclic tests to 750- and 1,000-psi pressure levels with varying dwell times 

 at maximum and minimum pressure. Since no damage in the model was 

 observed prior to placing it in the regular cycling program, the effects of 

 prior cycling history on the test results generated in the regular cycling pro- 

 gram were considered insignificant. All of the models used for cycling tests 

 were equipped with tie rods. 



104 



