As shown in Figure 12, Model EC-IA sustained a pressure of 1650 psi prior to failure 

 of the missile tubes. There was no visible damage to either the shell or frames as can be 

 seen in Figure 13, which indicates that the tubes were not adequately designed to withstand 

 the loads imposed upon them by the oval shell. 



Model EC-IB, a model of the same length as EC-IA but without missile tubes, failed 

 at a pressure of 1670 psi. Failure appeared to be attributed to a tendency of the oval cross 

 section to "flatten out"; see Figure 14. 



Strain-sensitivity factors for each gage on Models EC-IA and EC-IB are given in 

 Figures 8 to 11. 



DISCUSSION AND INTERPRETATION OF RESULTS 

 EFFECT OF BULKHEAD SPACING 



Table 1 compares the measured stresses obtained from the original-length model (EC-1) 

 and a half-length model (EC-IB). The circumferential flange stresses and the Hencky-Von 

 Mises shell stresses (midbay) given in Table 1 for the major and minor axes of both models 

 represent average values determined from strain gages located at similar locations. It can be 

 seen that the Hencky-Von Mises shell stresses near the region of the major axis and the 

 flange stresses were appreciably reduced by closing the distance between rigid bulkheads. 

 Figures 15 and 16 compare both the circumferential and longitudinal stresses for a quadrant 

 of the shell at midbay of Models EC-1 and EC-IB, The abscissa d in these figures is the 

 angle which a normal to the median surface of its shell in Figure 1 makes with the major axis. 

 It can be seen from Figures 16 and 16 that the shell stresses measured on Model EC-IB were 

 appreciably influenced by the rigid closure bulkheads. 



EFFECT OF MISSILE TUBES 



Table 2 compares the measured stresses obtained from the oval cylinder with missile 

 tubes (EC-IA) and a similar cylinder without missile tubes (EC-IB). Stresses given for 

 Model EC-IA are those away from the region of the missile-tube penetrations. It can be seen 

 that the "strut" action afforded by the tubes reduced the overall stresses of the oval cylinder 

 considerably. 



The highest stresses measured on Model EC-IA were not those shown in Table 2. 

 Higher stresses were measured on the inside surface of the shell at the intersection of the 

 center tube; a principal-stress value of -71.9 psi/psi was determined from strain gages 

 located in this region. Another area of high stress was that measured on the missile tubes 

 away from the shell intersection; an axial stress of -63.3 psi/psi was measured on the center 

 tube. It is interesting to note that neither of these stresses was as high as the highest 

 measured stresses which were found on the frame flange of the original model (EC-1); see 

 Table 1. 



