An axial compression test was performed on a single model capsule 

 by pretensioning the internal tie rods connecting the polar metallic end 

 plates. The objective of this test was to establish experimentally how 

 serious the stresses would be in the acrylic plastic hull if the pretensioned 

 tie rods were utilized in the capsule to place it under precompression prior 

 to lifting it off the deck during launching operations. To simulate actual 

 lifting operations, the tie rods inside the model were pretensioned to exert 

 a total force of 100 pounds — equal in magnitude to the weight of the pod 

 and anchor required for a 15-inch NEMO system. Since the weight of the 

 pod and anchor increases with the cube of the diameter, while the wall 

 section increases as the square of the diameter, the strains from testing the 

 model would have to be scaled up for prediction of strains in larger capsules. 



Testing the Large-Scale Capsule. Although the 66-inch large-scale 

 capsule was also tested hydrostatically, there was a distinct difference 

 between testing it and the model capsules described previously. While for 

 the testing of models an attempt was made to provide a separate model for 

 each kind of test, only one large-scale capsule specimen was available for the 

 whole series of tests planned for the large-scale prototype. For this reason, 

 the test results generated with the single large-scale capsule must be consid- 

 ered from the purely experimental viewpoint to a large measure as qualitative 

 rather than quantitative. From the operational viewpoint, the fact that a 

 single hull has been subjected to a diversity of tests is of course desirable, 

 rather than objectionable because, during the operational life of a functional 

 NEMO system, the capsule will also be subjected to a diversity of hydrostatic 

 loading conditions. 



All the hydrostatic tests on the large-scale capsule were performed in 

 NCEL's 72-inch-diameter pressure vessel (Figure 70) which has a 5,500-psi 

 pressure rating. Since the prime objective of the testing program for the 

 single large-scale capsule was to generate a maximum of data in the shortest 

 period of time without imploding the hull, only tests of short duration 

 (24 hours or less) were performed, as they satisfied both requirements of 

 the test program. 



The pressurization rate for all the tests (Table 7) was selected to be 

 100 psi/min, identical to the pressurization rate applied to the capsule models. 

 The maximum cycle pressure and temperature of the pressurizing medium 

 varied from 100 to 1,070 psi and 32 to 70°F, respectively. For most of the 

 tests, the interior of the hull was dry and open to atmospheric pressure; for a 

 few of the cycling tests the interior was filled with water, which was vented 

 to the atmosphere. 



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