would be permanently deformed. Only lithium and syntactic foam have a bulk 

 modulus greater than that of water. 



HYDROSTATIC TESTS AND HYDROSTATIC TEST FACILITIES 



In order to determine the effect of simulated service conditions on 

 the syntactic foams, some specimens were subjected to hydrostatic pressures 

 of 10,000 psi for 1000 hours. Other specimens were subjected to 1000 

 cycles of hydrostatic pressure between atmospheric and 10,000 psi. 

 Figure 3 shows a view of the NASL hydrospace test facility. This consists 

 of four pressure vessels, which are modified 16 inch Naval projectiles, 

 with auxiliary piping and instrumentation. Two of the pressure vessels 

 are used at test pressures to 10,000 psi, these are not shielded. The 

 other two vessels, with the shielding, are used at pressures up to 

 25,000 psi. Figure 4 shows a cross section of one pressure vessel and its 

 auxiliary piping. The vessels may be held at a designated pressure or may 

 be cycled between two pressures for selected time intervals. 



Water Absorption 



Static Exposure 



Figure 5 shows a graph of the water absorption of several types 

 of syntactic foam after exposure to hydrostatic pressure of 10,000 psi for 

 periods of immersion up to 1000 hours. In addition to ML-B3, two earlier 

 formulations, ML-B2 and ML-Bl, and a commercially available syntactic foam 

 are shown. Each week the pressure was released, the specimens were re- 

 moved, blotted, weighed and measured. The specimens were then replaced 

 in the pressure vessel and the test was continued. The epoxy-resin 

 hardener system was identical in each of the Applied Science Laboratory 

 foams. The hollow glass sphere filler however differed. It should be 

 noted that the specimen size for each group was 2x2x1 and that each 

 specimen had cut or milled faces. The effect of specimen size, and the 

 effect of a residual molded "skin" on water absorption will be discussed 

 later. 



Cyclic Exposure 



Figure 6 shows water absorption of several syntactic foams; 

 after exposure to 1000 cycles of pressure between atmospheric and 10,000 

 psi. Each cycle lasted 20 minutes. Tlie pressure was raised from atmos- 

 pheric to 10,000 psi. during a four minute period and was held at this 

 pressure for 12 minutes, then released in several seconds. The pressure 

 was then held at atmospheric for four minutes and the cycle was repeated. 

 Specimens exposed to this cyclic exposure showed a slightly higher water 

 absorption than those subjected to continuous static exposure at 10,000 

 psi for 1000 hours. The increased water absor])tion and slightly lower 



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