of tests, the interior of the hull was kept dry and vented to the atmosphere. 

 Ambient temperatures of the hull interior and exterior were maintained in 

 the 68 to 72°F temperature range. 



Displacement changes of the hull were investigated by a series of 

 tests in which the pressure was varied from 250 to 750 psi. In each of the 

 tests, the pressure was raised to the desired maximum pressure level, held 

 there for 6 hours, and then followed by a depressurization and relaxation 

 period of 18 hours. For those tests, the interior of the hull was filled with 

 water vented to the atmosphere. During the pressurization of the hull, 

 water was displaced from it because of the hull contraction, and the quan- 

 tity of displaced water was used as a measure of hull contraction. The 

 ambient temperatures both in the exterior and interior of the hull were in 

 the 68 to 72°F range. Upon depressurization, the water displaced from 

 the interior was siphoned back into the vessel interior, giving a measure of 

 capsule relaxation during depressurization. 



The effect of differential temperature on the strains in the hull was 

 evaluated in a series of cyclic pressure tests from to 500 psi with the dwell 

 time at 500 psi being 4 hours and the relaxation time 20 hours. The temper- 

 ature of the water surrounding the capsule was varied from 60 to 32°F, while 

 the ambient temperature of the dry interior varied from 79 to 45°F. Because 

 of the difference in internal and external ambient temperatures, a temperature 

 gradient existed inside the wall of the acrylic plastic hull (Figure 71 ). 



In addition to the tests to 500 psi, one brief test was run to 1,070 psi 

 and another to 1,000 psi. Besides showing the capability of the hull to with- 

 stand a pressure 300% greater than the rated capability of the hull, these tests 

 also supplied information on the strains in the hull at very high stress levels 

 and the rate of relaxation after depressurization from such high excess pres- 

 sures. The scale effect for crack-sensitive materials was determined by 

 imploding the 66-inch capsule and comparing its short-term implosion 

 pressure with the short-term implosion pressures previously determined by 

 imploding 1 5-inch small-scale models. This test completed the testing program 

 for the 66-inch prototype capsule. 



Instrumentation 



Long-term and cyclic tests on the 15-inch capsule models used only a 

 minimum of instrumentation as it was not feasible to tie up electronic equip- 

 ment for more than 1 year just for these tests. The instrumentation for almost 

 all model capsules under long-term or cyclic pressure testing consisted only of 

 temperature and pressure gages, from which data were read and recorded 3 

 times daily. The failure of the models was noted by a sudden drop in pressure. 

 If failure did not occur prior to the termination of the test, the model was 

 then carefully inspected upon removal from the vessel to ascertain the level 

 of damage to the hull. 



109 



