static loading; hence, the geometry was the same as that of Model IL. How- 

 ever, it was decided that Model lA could be of greater value if it were 

 tested cyclically. The ratio of weight of material to weight of displace- 

 ment for a typical section was. 0.53. 



Model DSRV-IF was constructed of cylindrical segments of 7079-T6 

 aluminum with a yield strength of 72,000 psi and a jacket of HY-100 steel 

 with a yield strength of 105,000 psio Its geometry (excluding the jacket) 

 is about 7 percent lighter than the 7079-T6 aluminum elements of Model 

 DSRV-IA. The original model included a thinner steel jacket; however, 

 this jacket failed after 12 pressure cycles had been applied. Subse- 

 quently, upon reassembly of the model, more care was exercised in welding 

 a thicker jacket to provide more stability. The heavier jacket is the one 

 depicted in the drawings and referred to hereafter. The closures and 



penetrations incorporated in Model IF were designed using results of earlier 



3 

 static tests of closure models. This model weighed 58.7 percent of its 



displacement. Figure 1 is a sketch of Models DSRV-IA and DSRV-IF. Pene- 

 trations in the cylindrical portion of Model IF were oriented 30 deg apart. 

 For illustrative purposes. Figure lb shows them to be on line. Figure 2 

 shows Model DSRV-IF after fabrication. 



Using data from Reference 2 and correcting for differences in jacket 

 material and disparities in yield strengths, a collapse depth of about 

 15,000 ft was calculated for both models. 



TEST PROCEDURE AND RESULTS 



Prior to cyclic testing, both models were instrumented with foil 

 resistance gages for static loading. The static and fatigue tests were 

 conducted at the Southwest Research Institute (SRi) at San Antonio, Texas. 

 Strain data were recorded while the models were pressurized in the SRI 

 4-ft pressure tank. Two pressure runs to 3500 psi were made for each 

 model. Figure 3 shows strain gage locations and strciins extrapolated to 

 4450 psi. Next, the models were placed in a 30-in. -diameter tank and sub- 

 jected to a pressure of 4900 psi, a 10 percent overload. During this test, 

 the light steel jacket on Model DSRV-IF buckled. However, it was decided 

 to continue with the cyclic test of this model and both models were placed 

 in the SRI cyclic tank. The models were filled with oil and surrounded by 



