known "flat spots" and "thin spots" were machined and tested. A sketch of 



these models is shown in Figure 6. The ratio of h/R and the angle 4> were 



varied systematically. A detailed description of the models and analysis 



of the results is presented in Reference 6. Briefly, the collapse of these 



models was predicted using the local geometry over a critical arc length 



as described above. A comparison of the experimental results and the 



pressure predicted by Equation [8] is presented in Figure 7. The ordinate 



is the ratio of p to p' , and the abscissa is the ratio of p' to p_ . It 



is apparent that this procedure adequately predicted the collapse of these 



shells. The apparent experimental scatter for the less stable shells 



(p'/p' ^ 0.7) can be explained on an individual basis. The collapse 



pressures of those models which fall below the line were affected by 



secondary moments. The curves shown in Figure 3 indicate that secondary 



moments significantly reduce the collapse pressures of the less stable 



shells. These effects diminish as the shells become more stable. For those 



models which lie above the line, the experimental buckling pressure was 



more than 70 percent of the classical pressure. Recent tests indicate 



that it may be possible to achieve 100 percent of the classical 



pressure. 



In addition to the machined models with inqjerfections, models of 



HY-80 steel fabricated according to feasible large-scale fabrication 



7 

 techniques are being studied. The local geometry is determined from 



thickness and sphericity measurements and is used to determine the stresses 

 and collapse pressures. Although the tests have not been completed, the 

 preliminary results indicate good agreement with the analysis presented 

 above. 



The model tests and results just described have been presented 

 briefly in order to provide a backgroimd for the evaluation of the ALVIN 

 pressure hulls. A more detailed description of the test results is given 

 in the references cited. 



DESCRIPTION OF ALVIN PRESSURE HULL 



The ALVIN pressure hull (see Figure 1) is composed of two spun HY- 

 100 steel hemispheres. The inside contour of each hemisphere was machined 



