which might possibly have been influenced significantly by the slot welds 

 in the adjacent areas. 



MODELS OV-3, OV-4, ANDOV-5 



The experimental collapse pressures for each of the three machined 

 titaniunn models were: 



Model 



OV-3 

 OV-4 

 OV-5 



Collapse 



Pressure 



psi 



12,700 

 11, 100 

 12,000 



Figures 16, 17, and 18 are photographs showing the mode of collapse for 

 each model. A catastrophic failure was observed for Model OV-3. It ap- 

 pears that axisymmetric yielding of the shells between the web stiffeners 

 may have been a contributing factor to collapse. Some permanent defor 

 mation in the form of an axisymmetric corrugation between the webs on 

 both the inner and outer shells was visible over the entire structure. 



Model OV-4 failed by general instability in an oval (n = 2) mode with- 

 out any rupturing of the shell elements. Unlike Model OV-3, permanent 

 deformations between adjacent webs were observed only in limited regions 

 of the structure. 



Model OV-5, like OV-4, failed by general instability; however, 

 there was a marked difference in the appearance of the failure. In addi- 

 tion, permanent deformations between adjacent webs were visible over 

 the entire structure. 



21 



