hull could be even lower. On the basis of these results it can be concluded 

 that the original design would prove inadequate in meeting the minimum 

 specified collapse pressure of 10,000 psi. 



When the observed collapse pressure of Model OV-5, incorporating 

 the suggested redesign in a long cylinder length, is extrapolated to a yield 

 strength of 120,000 psi, a pressure of 11,290 psi is obtained. This is 13 

 percent above the mininaum specified. The question as to whether this 

 represents an adequate margin for the fabricated hull remains unanswered 

 at the present. In addition, the question of fatigue strength for the sand- 

 wich hull may be of some concern since stresses on the order of 90 per- 

 cent of the minimum specified yield strength (120, 000 psi) at an operating 

 depth of 15, 000 ft are indicated by the analysis of Reference 3. 



Before any final conclusions can be drawn concerning the adequacy 

 of the suggested redesign, it will be necessary to test larger scale tita- 

 nium models which are fabricated to be identical in all respects, except 

 size, to those anticipated in the prototype. This should be done so that all 

 factors which appear to influence static and fatigue strength are adequately 

 considered. At this stage of the preliminary design studies, it can only be 

 said that the OV-5 redesign may represent a possible hull structure for 

 the proposed oceanographic vehicle. 



CONCLUSIONS 



1. The test results obtained with the one -diameter -long model 

 (OV-3) indicate that the interbay strength of the original sandwich hull 

 design exceeds the desired collapse pressure of 10,000 psi. Also, the 

 construction technique of slipping the outer shell over the integral web- 

 and-inner- shell assembly, without physically joining the webs to the outer 

 shell, does not appear to prejudice structural strength. The test results 

 obtained with the four -diameter -long model (OV-4) indicate that the crit- 

 ical mode of failure is one of inelastic general instability and that the 

 original design is not adequate to satisfy the minimum specified collapse 

 pressure . 



33 



