UNDERSEA TECHNOLOGY 



43 



Three-foot-diame ter glass-reinforced 

 plastic deep-submergence pressure hull 

 model awaiting hydrostatic pressure test. 

 This model was hydrostaticaUy tested 

 to failure at 11,500 psi, equivalent to 

 approximately 25, 000- ft depth. 



Much development work remains to be done before this material can be 

 considered for a manned pressure hull. Problems such as interlaminar 

 shear, fatigue, water absorption, fabrication scale-up, and nondestructive 

 test methods and standards are being investigated. 



A reinforced plastic cannot be characterized as a homogeneous material 

 because it does not behave as a composite material until a structural ele- 

 ment has actually been fabricated. Therefore, it is difficult to divorce 

 structural response from performance characteristics of the material. 



New reinforcing fibers such as carbon fibers and high-strength metal 

 fiber, as well as improved plastic matrix materials, are being developed. As 

 a result improvements in the overall performance of composite materials 

 for deep-submergence hulls are expected. 



Radial-fiber spheres uniquely utilize glass-reinforced plastic. Spheres are 

 fabricated by a process which results in radial orientation of aU glass mono- 

 filaments held in place by an epoxy resin matrix. Compressive stresses of 

 200,000 psi have been achieved in these structures without failure. 



Massive Glass 



Because glass is almost perfectly elastic, and completely brittle, there 

 are formidable problems in design, fabrication, and testing. While the 



