DISCUSSION 



The measured strains, presented in Figure 3, are compared with 

 theoretical strains in Table 1. The agreement with theory is very good, 

 indicating that the elastic strains were not affected by the structural 

 discontinuities at the frames. The calculations are from the theory of 



r 7 



Salerno and Pulos as presented by Lunchick and Short. 



All of the models failed by inelastic general instability in the 

 n=2 mode. This is indicated by the appearance of the models after test 

 (Figure 4) as well as by the theoretical calculations. The computed 

 collapse pressures for Models PJ-1S and PJ-1L indicate a very high degree 

 of stability in the elastic shell buckling modes and a margin of at least 

 20 percent in the inelastic shell buckling modes; see Table 2. 



Because of the highly stable shell design, the theoretical in- 

 elastic shell buckling pressures ' ' correspond to strain levels in excess 

 of those measured in tests of material compression specimens. The ratios 

 reported in Table 2 correspond to average strain levels of 1.5 percent. No 

 theory is available to compute the shell-buckle pressures for nonuniform 

 shells such as those of Model PJ-2. All of the theories presented in 

 Table 2 assume the models to be of monolithic construction. 



The experimental collapse pressures and the scaled collapse strengths 

 are given in Table 3. To compare the ring models with monolithic hulls, 

 data from two other models are also included in Table 3. Model DSRV-P 3 

 a small machined-aluminum model, similar to Model PJ-1S was 1.4 diameters 

 long and had a modified-Bryant critical buckling pressure of 3.55 times its 

 collapse pressure. Since it is impossible to machine a monolithic sandwich 

 hull such as Model PJ-2, a similar two-piece hull is included in this 

 discussion for comparison. Model OV-4 was made by inserting a cylinder 

 with outside rectangular frames into a closely fitted jacket, which formed 

 the outer shell. Model OV-4 11 had nearly the same semi-infinite, elastic, 

 general-instability collapse pressure as Model PJ-2 and was 4 diameters 

 long. 



