Fig. 2. Hollow aluminum cylinders in plastic 

 as photographed 2 hours after removal 

 from pressure tank following 6 months 

 exposure to 9>°00 psig- 



Fig. 3- Hollow aluminum cylinders in plastic 

 as photographed 5 days after removal 

 from pressure tank following 6 months 

 exposure to 9)000 psig. 



From this test we know that long term pressure 

 tests must he integrated into the overall environ- 

 mental simulation tests. It is essential to 

 determine the characteristics of various resins 

 and fillers with respect to cold flow if success- 

 ful operation of potted circuits without heavy 

 metallic pressure housings is to he achieved. 



In a 2-week test a number of resistors and 

 capacitors were placed in the tank under 10,000 

 psig and at room temperature. The resistors 

 tested were of a type in which a glass encapsula- 

 tion is fusion sealed around a tin oxide resis- 

 tance element. Sixty percent were unaffected by 

 the test, 20$ leaked but still read correct resis- 

 tance, 10$ developed encapsulation cracks but 

 still read correct resistance and 10$ broke and 

 were completely unusable. 



The capacitors tested were of a ceramic type 

 and their capacitance, in most cases, had 

 decreased enough to cause concern at the conclu- 

 sion of the 2-week test. These same capacitors 

 were placed into a long term pressure container 

 and the pressure held for 2 months. When the 

 capacitors were removed from the test most of 

 the capacitors had increased their capacitance. 

 What seems most unusual is that the capacitance 

 increased more in the 2-month test than the 

 capacitance decreased in the 2-week test. Mea- 

 surements were again made after the capacitors 

 had 2 days in the atmosphere to recover. The 

 larger valued capacitors returned almost to their 

 original value but the lower values were still 

 reading high although they did show some recovery. 



An important discovery in this test is that 

 all components must be tested carefully under 

 many conditions. An instrument designed and con- 

 structed with certain of these ceramic type com- 

 ponents would have become unreliable sometime 

 after lowering. 



HOLLOW VESSEL TESTS 



A typical test method for determining the 

 external burst pressure of an air filled vessel 

 is to place it in a fluid filled pressure tank 

 and build up the pressure until the test vessel 

 implodes . This technique does give the desired 

 answer but usually cannot show how or where the 

 failure began. 



A method which is now being used at the Naval 

 Eesearch Laboratory does not take the test vessel 

 to complete destruction. The unit is filled with 

 fluid and a small, say 0.025 inch inside diameter 

 tube is inserted into the vessel (Figs, k and 5) 

 and led out of the pressure tank. This tube is 

 led into an upright or inclined manometer tube, 

 open at the top. As pressure is applied on the 

 test vessel, it will shrink slightly, forcing the 

 fluid up the glass tubing. This gives a dynamic, 

 instantaneous and accurate measure of the test 

 item's deflection. If the deflection is measured 

 and plotted against pressure as the test proceeds 

 then material yield points are easily recognized 

 and the test stopped if desirable. On the other 

 hand, if carried to burst pressure, the resulting 

 implosion is stopped far short of complete col- 

 lapse, due to the back pressure occurring within 

 the test vessel, since the thin 0.025 inch tubing 

 will not allow the inside fluid to be squeezed 

 out fast enough. A view of the deflection in an 

 aluminum sphere is shown in Fig. 6. Other samples 

 have been tested using this technique and analyses 

 conducted. Figs. 7 an< i 8 are pictures of 



Fig. h. 



Aluminum sphere with manometer 

 needle attached. 



170 



