Models OV-3, OV-4, and OV-5 were tested under external hydrostat- 

 ic pressure in relatively smail-size pressure tanks so as to resttict the 

 extent of failure and thus to better determine the mode and point of initia- 

 tion of failure. A light-grade oil was used as the pressurizing medium. 

 These models were each tested in two pressure runs. For the first run, 

 pressure was increased in increments of 500 psi until a maximum pres- 

 sure of 5000 psi was reached. Each model was rennoved from the tank at 

 the conclusion of its first run and was visually inspected for any possible 

 leakage of oil into the inside of the model. For the second run, each mod- 

 el was pressurized to 5000 psi and pressure was then increased in incre- 

 ments of 100 psi until collapse occurred. The pressure was maintained 

 for Z min at each pressure interval for Models OV-3 and OV-4 and for 

 1 min for Model OV-5. 



TEST RESULTS AND DISCUSSION 



MODELS OV-1 AND OV-2 



The ultimate load-carrying capacity of both Models OV-1 and OV-2 

 was 11,700 psi. The failure of Model OV-1 was restricted to an axisym- 

 metric crease extending almost completely around the entire circurafer- 

 ence between Webs 1 to 12. Figure 12 shows the mode of collapse. The 

 collapse mode for Model OV-2 was one of apparent general instability in 

 which a longitudinal crease extended almost the entire length of the model; 

 see Figure 1 3 . 



Strain- sensitivity factors for each gage determined by averaging the 

 results from each of the pressure runs are shown in Figures 10 and 11 

 for Models OV-1 and OV-2, respectively. Also given are the theoretical 

 strains computed using the elastic analysis of Reference 3 for a typical 

 bay of the sandwich cross section. The measured strains in the center 

 region of both models compared favorably with the corresponding theoret- 

 ical value, except that there was an appreciable variation in the observed 

 circumferential strains in the outer shell at the toe of the webs of Model 

 OV-1. This probably can be attributed to local distortion due to the slot- 

 welding. 



17 



