ABSTRACT 



Out-of -roundness measurements were taken on three 

 spherical pressure hulls which have been fabricated for ALVIN, 

 a two-man oceanographic vehicle designed for an operating 

 depth of 6000 ft. The results of these measurements in- 

 dicated that over a critical arc length, the maximum ratio of 

 local radius to nominal radius was 1.05. The collapse 

 strength of the three hulls was evaluated by means of a 

 recently developed analysis which utilizes local geometry as 

 determined by out-of -roundness measurements . Based on 

 critical local geometry and available stress-strain curves, 

 the analysis indicated that the collapse depths of the hulls 

 ranged from approximately 15,000 to 16,000 ft. A high degree 

 of confidence is placed in the results, and the importance 

 of accurately measuring the shape of spherical shells is 

 emphasized. 



INTRODUCTION 



The use of the spherical shell as a pressure hull configuration is 

 receiving a good deal of attention in the Navy for deep-depth application. 

 The research vehicle TRIESTE, which has descended to depths of 35,000 ft, 

 utilizes a spherical shell as a pressure hull. Other oceanographic re- 

 search vehicles currently being fabricated or in the design stage also use 

 this type of structure as a pressure hull. In addition, the ends of deeper 

 diving submarines having basically cylindrical middle bodies will probably 

 be closed with hemispherical shells. 



Historically, the design of the spherical shell has been hampered 

 by the lack of agreement between theory and experiments. Because of Navy 

 interest in this type of structure, the David Taylor Model Basin engaged 

 in an extensive experimental program to investigate this disagreement and 

 to develop reliable design criteria for spherical shells. This program in- 

 cludes studies of near-perfect machined shells, machined shells with im- 

 perfections, and shells fabricated according to feasible full-scale fab- 

 rication techniques. The effects of flat spots, thin spots, mismatch, 

 penetrations, stiffeners, and residual stresses are being studied. Although 

 this investigation is by no means complete, a number of important conclusions 



