to size and the two hemispheres were welded to form the complete sphere. 

 The outside contour was machined after welding. Five large penetrations 

 were made in the completed hull and the reinforcement inserts were welded 

 in place. After all welding, the hull was stress relieved. Three hulls, 

 designated Hull No. 1, Hull No. 2, and HuJ.l No. 3, were fabricated. 



Typical compressive stress-strain curves for the HY-100 steel 

 material used in the fabrication of the hulls are shown in Figure 8. These 

 curves were obtained from tests of specimens machined from the material re- 

 moved for the penetrations. Specimen coupons were obtained from the 

 material removed from the hatch and from a viewing port (Window No. 3). 

 Thus, the curves of Figure 8 represent each of the hemispheres used in 

 manufacturing the hulls. Other representative material characteristics 

 are presented in Figure 9. 



Hull thickness measurements provided by Hahn and Clay are presented 

 in Figure 10. These measurements were made by vidigage after the welds 

 had been ground. 



MEASUREMENTS OF INITIAL IMPERFECTIONS 



Initial imperfections and fabrication tolerances were important 

 considerations in the design of this vehicle. A maximum radius of cur- 

 vature of 45 in. was specified as a reasonable fabrication tolerance. 

 After fabrication, it was necessary to take out-of-roundness measurements 

 to determine the maximum radius of curvature over a critical arc length. 

 This information is valuable not only in evaluating the ALVIN pressure 

 hulls but also in determining feasible fabrication tolerances for similarly 

 fabricated vehicles . 



The instrument shown in Figure 11 was designed to take sphericity 

 measurements from a common point for the completed ALVIN hulls. Basically, 



Six specimens were tested for each hull. The total variation in yield 

 strength for each hull was only 4 percent. 



The hull thickness measurements presented in Figure 10 were used in all 

 strength calculations. No allowances were made for corrosion. 



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