Projections for increases in compressive strength properties as 

 well as other properties are based on the following considerations: 



A 50 per cent improvement in resin compressive strength by 1970. 

 Polyester and epoxy resin systems having 30,000 psi compressive yield 

 strength representing an increase of 50 per cent over the present strength 

 are now under laboratory investigation. 



A 50 per cent improvement in the strength of newly available glass 

 and ceramic materials which may be used as hollow sphere filler, and the 

 development of better coupling agents and fabrication technology. 



Other Strength Properties 



An increase in the strength of the resin, and hollow spheres and 

 an improvement in fabrication procedures can be expected to improve other 

 properties such as tensile, shear and fatigue strengths. 



Density 



Development of resin systems having either higher strength or lower 

 density or both, and of stronger and more uniform low density fillers will 

 result in lower density buoyancy materials than those cited in Table 3. 

 Figure 8 projects improvements in buoyancy for 3 types of materials. The 

 use of larger size hollow glass spheres, up to several inches outside 

 diameter, in a syntactic foam matrix offers opportunities for density re- 

 duction. To produce an optimum material, one with highest buoyancy, the 

 problem of relative sphere size, sphere thickness and spacing of spheres 

 in the matrix is being studied both mathematically and experimentally. 

 The Naval Applied Science Laboratory is now investigating the use of large, 

 coated glass and ceramic spheres distributed in a syntactic foam matrix 

 with a target of developing a buoyancy system with a density of 25 pcf and 

 capable of withstanding a pressure of 13,500 psi. 



Costs 



The present 44 pcf syntactic foam suitable for use at 10,000 psi 

 hydrostatic pressure ranges in price from $4.00 to $9.00 per pound de- 

 pending on quantity used; the price per pound of net buoyancy is between 

 $8.00 and $18.00. These values are based on resin system costs of approxi- 

 mately $0.90 per pound, glass spheres at $5.00 to $12.00 per pound plus 

 fabrication costs. Lower strength spheres which may be suitable for use 

 up to 5000 psi are available at a price of $0.65 per pound. Figure 8 

 shows projected costs for 3 types of buoyancy materials. The most promi- 

 sing area for decrease in the price of the higher strength syntactic foam 

 is the reduction in manufacturing costs of the highest priced ingredient, 

 the glass sphere filler. This may be expected, if and when, there is a 

 substantial increase in demand for the material. 



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