buoyancy materials. Ultimately it will be desirable 
to develop a buoyancy material providing 39 to 44 
pounds of lift per cubic foot for 20,000-foot 
operations. Syntactic foam improvements may 
require stronger, lighter resins and microspheres 
with improved tolerances and fatigue life; the 
possible combination of glass macrospheres and 
microspheres in the foam matrix; and castable 
foams that can be poured into small irregular 
spaces and set at room temperature. To use glass 
spheres, techniques must be developed to elimi- 
nate the danger of sympathetic implosion, a very 
serious problem prohibiting their use currently. 
A possible assist may come from development 
of structural members which are themselves posi- 
tively or neutrally buoyant. For example, an outer 
skin built of laminated GRP imbedded with glass 
microspheres might be used both to reduce wet 
weight and to add stiffness to the outer hull 
structure. Effort devoted to improving buoyancy 
materials and developing buoyant structure is sure 
to be highly cost effective and could even permit 
less advanced pressure capsule materials in 20,000 
foot systems. 
5. Secondary Materials 
There are a great number of critical secondary 
materials problems for undersea structures, vehi- 
cles, and devices. They involve rubber, plastics, 
fabrics, fibers, insulations, hydraulic fluids, lubri- 
cants, etc. The problems are related to such 
environmental effects as leakage under pressure, 
temperature embrittlement, corrosion, fouling, 
scouring, and contamination. Most materials devel- 
oped for submerged use have been employed only 
near the surface. Research and development on 
deep sea materials has barely begun. 
6. Conclusions 
Materials technology development is of critical 
concern, and upon it the economy and effective- 
ness of undersea activities depends. Weight-to- 
displacement pressure hull ratios of 0.4 to 0.6 are 
exceedingly important due to the fundamental 
requirement of supporting the remainder of the 
vehicle to achieve neutral buoyancy. 
If the pressure capsule cannot provide needed 
buoyancy, supplemental material must be added, 
increasing vehicle weight and cost, and reducing 
effectiveness. Materials considered for structural 
applications include steel, titanium, aluminum, 
glass, glass fiber reinforced plastics, and ceramics. 
All have promise of meeting low W/D ratios at 
20,000 feet by 1980. 
Although such materials as titanium and glass 
are being improved, once manufacturing and fabri- 
cating techniques have been developed the high 
strength steels might remain least costly for most 
undersea applications. Materials failures in marine 
equipment, a major shortcoming of most oceano- 
graphic efforts, may constitute a major obstacle to 
better utilization of the sea. Fatigue life under 
cyclic stress is important in selecting materials for 
submersibles, and long-term corrosion is the key 
consideration for permanent structures. 
Extensive use of supplemental buoyancy mate- 
rial for operations below a few thousand feet is 
likely to be required for many years. Currently for 
20,000-foot operations, buoyancy materials give 
only about one-half pound of buoyancy for each 
pound of their own weight. Vehicle volume has an 
important effect on maneuverability, and the 
buoyancy material has. an important effect on 
vehicle weight, volume, and costs. Hence, im- 
proved buoyancy materials and equipment will be 
very cost effective. 
Independent or contractual materials develop- 
ment is not being undertaken to a meaningful 
extent by industry. For example, 80 per cent of 
the Navy’s exploratory development in deep ocean 
materials is undertaken in-house. 
Recommendations: 
Structural materials development must be acceler- 
ated along several paths with sufficient funds to 
reach fair conclusions about the ability to obtain 
efficient deep submersible and habitat structures. 
After 10 years, efforts should be narrowed and 
production choices made. Research must be coor- 
dinated and industry initiative encouraged; the 
approach should be through systems engineering. 
Efforts should focus on: 
—Steel. High strength steels development and 
fabrication techniques, including study of fatigue 
problems, should be pushed to obtain a high- 
quality , low-cost material. 
—Nonferrous metals. Aluminum and _ titanium 
should be developed to provide the basis for 
efficient (W/D=0.4 to 0.6) 20,000-foot structures 
VI-45 
