44 THE NAVY OCEAN ENGINEERING PROGRAM 



theoretical tensile strength of massive glass is on the order of 1,000,000 psi, 

 the practical tensile strength of massive glass is very low. 



This apparently contradictory situation is due in part to flaws on the 

 surface of the glass which effectively reduce its strength. Surface-removal 

 experiments have confirmed the surface-flaw theory. The surface of soda- 

 glass rods 6 to 8 mm in diameter was carefully ground, which increased the 

 tensile strength from 12,000 psi to over 400,000 psi. In order to retain 

 the strength, the ground surface must be carefully protected. 



Another technique for increasing the tensile strength of glass is to place 

 the surface in compression by chill tempering or by an ion-exchange proc- 

 ess. In this way, the material can withstand tensile loading, the amount de- 

 pending upon the process and depth of the surface layer. 



BUOYANCY MATERIAL 



In order to develop a low density material to be used for auxiliary 

 buoyancy for deep-submergence vehicles, the Navy is investigating a number 

 of approaches: syntactic foam, hollow massive glass spheres/ syntactic foam 

 modules, and radial-fiber-reinforced plastic spheres. 



Syntactic foam consists of extremely small hollow ceramic or glass 

 spheres having an outside diameter of 20 to 90 microns embedded in a 

 plastic matrix. This material in a bulk form has a density of 42 to 46 lb 



EXPLODED VIEW OF 

 TENTATIVE MODEl 



LARGE HOLLOW . ^„ , _. 



SPHERES ---^ -;^)r . 2Hydrostatic 



SYNTACTIC FOAM 

 MATRIX 



TARGET PROPERTIES 

 I.Net buoyancy,pcf- 36 



compressive 

 strength, psi -13,500 



Buoyancy module. Low-density materials are used as auxiliary buoyancy for 

 deep-submergence vehicles. This one is composed of a closely packed arrangement 

 of large hollow glass spheres (all larger than %-in. diameter), with the voids between 

 spheres filled with syntactic foam. 



