The model was designed using an end arrangement to preclude pre- 

 mature failure near the rigid closure bulkheads; see Figure 3. It was 

 made pressure-tight by welding heavy rings on each end and then attach- 

 ing a heavy closure bulkhead to each ring. 



MODELS OV-3 AND OV-4 



The next step in the sequence of developing background information 

 before going to some large-scale fabricated titanium models was to test 

 some small-scale machined titanium models which could be made imme- 

 diately at a very nominal cost. For this reason, Models OV-3 and OV-4, 

 representing one-diameter and four-diameter lengths, respectively, of 

 the original design, were built and tested. 



The dimensions and design details of Models OV-3 and OV-4 are 

 shown in Figure 4. Dimensional tolerances between the outer shell and 

 the webs were specified so that a maximum clearance of 0.0008 in. be- 

 tween these two elements would exist when the outer shell was slipped 

 over the inner shell-web combination. Figure 5 shows the component 

 parts of Model OV-4, prior to assembly. 



After each model was assembled, the ends of the cylinders were 

 ground flush to ensure proper distribution of the axial pressure load to the 

 inner and outer shells. The models were designed using an end arrange- 

 ment, as shown in Figure 4, to preclude premature failure near the rigid 

 closure rings. They were made pressure-tight by using a heavy plate and 

 an "0"-ring seal at each end. The closure plates were not physically at- 

 tached to the cylinder but were seated in place by the pressure. Figure 

 6 is an assembly drawing of Model OV-3. 



Models OV-3 and OV-4 were machined from a Zf -in. -diameter bar 

 of 6A1-4V c- titanium alloy. Sixteen compression specimens were taken 

 from the bar; the yield strength, based on a 0.2 -percent offset, ranged 

 from a low of 126, 000 psi to a high of 145, 000 psi with an average value 

 of about 138, 000 psi. Since the yield strength and stress -strain curve for 

 titanium alloys are sensitive to the rate of loading,^ these specimens were 

 tested at a rate corresponding to the pressure loading of the models. The 

 rate of loading was equivalent to a stress -intensity level of 550 psi/min, 



