INTERPRETATION OF RESULTS 



AXISYMMETRIC MODE OF COLLAPSE 



Table 2 gives "upper bound" theoretical collapse pressures p^ for 

 each model. These pressures are based on considerations of an equiva- 

 lent unstiffened cylinder having the same weight-displacenaent ratio and 

 material properties as the corresponding sandwich cylinder. Also, the 

 Hencky-Von Mises yield criterion was applied to the three-dimensional 

 state of stress at midplane, as determined from the Lame solution for a 

 thick-walled cylinder. The "upper bound" pressures computed in this 

 manner represent a state of complete stressing of the entire cross section 

 up to the value of yield strength used in each case. These calculations are 

 predicated on a plateau-type stress-strain curve, and the possibility of an 

 increase in the strength of the material due to strain-hardening is not con- 

 sidered. 



It can be seen in Table 2 that the aforementioned theoretical collapse 

 pressure p. is considerably lower than the observed collapse pressure for 

 each of the two steel models. Strain measurements taken during the tests 

 of OV-1 and OV-2 indicated that these structures were grossly strained 

 prior to collapse. 



TABLE 2 



Collapse Pressures 



Model 



Shell 



Yield 



Strength 



psl 



Material 



Approximate 

 Length- 

 Diameter 

 Ratio 



Experimental 



Collapse 



Pressure 



psl 



Three-Dlmenslonal 



State o£ Stress 



over Entire 



Material 



psl 



Elastic 

 General- 

 Instability 

 Pressure 

 psl 



Pc 

 Inelastic 



Experimental 



Collapse Pressure 



"Corrected" to 



Yield Strength 



of 120,000 psl 



General- 

 Instability 

 Pressure 

 psl 



OV-1 



112,500* 



Steel 



1 



11,700 



10,310 



100,000 





12,480 



OV-2 



106,300* 



Steel 



1 



11,700 



9,940 



101,000 





13,210 



OV-3 



138,000 



Titanium 



1 



12,700 



12,660 



51,000 



12,200 



11,040 



OV-4 



138,000 



Titanium 



4 



11,100 



12,660 



25,450 



11,250 



9,650 



OV-5 



127,500 



Titanium 



4 



12,000 



11,990 



51,000 



11,960 



11,290 



* Weighted value based on the relative circumferential membrane stresses In each of the outer and Inner shells. 



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