UNDERSEA TECHNOLOGY 



45 



per cu ft. The material has been tested to pressures equivalent to a 20,000 

 ft depth. 



The hollow massive glass spheres/syntactic foam material consists of 

 hollow spheres of various sizes (all larger than % in. in diameter) in a close- 

 packed arrangement. The voids between the spheres are filled with syn- 

 tactic foam which is cured to form a solid module. The larger spheres are 

 considered to be pressure hulls whose wall thickness is calculated to with- 

 stand the external hydrostatic pressure. The syntactic-foam encapsulation 

 may enhance this aspect as well as cushion the spheres from damage. This 

 material is more efficient than syittactic foam alone, because it provides a 

 larger air void per unit volume. Several problems remain unsolved: sym- 

 pathetic implosion of the close-packed spheres, reproducibiHty of the 

 spheres' collapse strength, and a means for nondestructive testing. 



Syntactic foam, one of the low-density materials being developed for use 

 as auxiliary buoyancy for deep-submergence vehicles. It is composed of hol- 

 low glass microspheres embedded in a plastic matrix and has a density of 40 

 to 46 Ib/ft^. 



