A few of the models were equipped with a volume change measuring 

 system to determine the magnitude of hull shrinkage under long-term loading 

 (Figure 72). This instrumentation system consisted of distilled water filling 

 the total interior volume of the model and tubing connecting the interior of 

 the model to an accurate graduate located on the exterior of the pressure 

 vessel. The shrinkage of the acrylic plastic hull under sustained pressure 

 caused water to flow from its interior into the graduate. Readings of water 

 level, temperature, and pressure were, at the initiation of the test, taken at 

 1-minute intervals for the first 15 minutes, every 5 minutes for the next 45 

 minutes, hourly for the next 7 hours, and 3 times daily thereafter until the 

 model failed or was depressurized. When the model capsule was depressurized, 

 the same data-recording process was repeated. 



Only two models were strain-gaged (Figure 73), and then only four 

 strain gages were used because of the limitation on the number of available 

 electric penetrations in the test pressure vessel. However, it was hoped that 

 by judicious placement of the strain gages a good representation of strain 

 distribution in the hull could be obtained. 



Short-term tests on model capsules utilized either strain-gage 

 (Figure 74), volume-displacement, diameter-contraction, or photoelastic 

 instrumentation. The strain-gage and the water-displacement instrumentation 

 systems were identical to those used in the long-term tests. The diameter- 

 contraction instrumentation consisted of a linear potentiometer inside the 

 capsule placed between the polar steel end plates and an externally located 

 read-out system calibrated to read in thousandths of an inch. The photo- 

 elastic instrumentation consisted of a light source inside the acrylic plastic 

 hull, circular polarizing sheets, a window in the pressure vessel end closure, 

 and a camera mounted on the exterior of the pressure vessel end closure 

 (Figure 75). During some of the tests, the camera was removed and visual 

 observations of the photoelastic interference fringes were made instead. 



Considerably more effort and expense were devoted to the 

 instrumentation of the large-scale capsule because ( 1 ) only a single capsule 

 specimen existed and (2) the testing of the large capsule was not as lengthy 

 as that of models so that complex electronic equipment could be tied up 

 for the tests. Some of the instrumentation systems were identical to those 

 used on the models, while others, such as the strain-instrumentation system, 

 were considerably more complex than a similar system on the model. The 

 instrumentation for measurement of strains consisted of 81 channels for 

 transmitting data generated by an equal number of electric resistance strain 

 gages mounted on the exterior and interior hull surfaces. Eastman 910 

 contact adhesive was found to work best for bonding the gages to the hull 

 and DOW Corning 105 silicone rubber with associated primer for subsequent 

 waterproofing. The strains were recorded digitally on paper by a 90-channel 

 BUDD DATRAN unit with a response capability of approximately 1 channel 

 per second. Considerable trouble was encountered in the procurement of 



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