materials such as low temperature and superconducting metals may offer 

 solutions. Another little understood parameter of conducting materials, 

 is their response to stresses imposed mechanically. High-voltage trans- 

 mission will also require improved dielectric materials. Gaseous die- 

 lectrics may ultimately provide the most cost-effective solution. 



Mechanical 



In contrast to the electrical design which is very specific for 

 the application, considerable latitude exists for the mechanical design 

 of an E-M cable. 



Materials . The most widely used material for the strength members 

 in E-M cables is steel, but the weight of steel is the one property which 

 generates the need for investigation of different strength member mater- 

 ials. The use of synthetics as strength members in E-w cables looks very 

 promising because of the following advantages: (1) high strength-to- 

 weight ratio; (2) extreme flexibility; and (3) resistance to corrosion. 

 Complete tradeoff analyses between the various synthetics and metallic 

 strength members have not been performed. This is presently very diffi- 

 cult because of the lack of data for svnthetics as E-M cable members. 

 Improved metal alloys and metals are not beyond the scope of application 

 in E-M cables, but those allovs and metals with the most desirable 

 properties, such as corrosion resistance, high strength and better fatigue 

 properties are presently too costly for most applications. 



Failure Mechanisms . A very deficient area which falls largely 

 under the mechanical function of the cable is the lack of understanding 

 in the area of failure mechanisms. Since most cable applications fail 

 due to some handling problem or to some mechanical property of the cable, 

 improvements in design, materials selection, and handling will follow 

 when the failures are pin-pointed and understood. Four problem areas of 

 E-M cable failures are kinking, fatigue, inadequate splicing techniques, 

 and low reliability of terminations. The kinking mechanism and the con- 

 ditions under which kinking occurs are not well understood. Fatigue 

 tests on various types of cable constructions and various materials have 

 not been made so that it is impossible to predict and compare the working 

 lives of E-M cables to develop selection criteria for the best cable for 

 a particular job. Analyses are also lacking in the area of dynamics, 

 snap loads, and rotational response of the cable to torque and tension, 

 elongation and creep, elasticity and fatigue strength. Seawater that 

 permeates the cable jacket and insulation causing hosing of water along 

 unblocked conductors to termination devices has been responsible for 

 many undersea system failures. 



Terminations 



Present cable terminations lack reliability even though there are 

 many suppliers of connectors and penetrators. Although these suppliers 

 can deliver the basic types of underwater connectors, stronger water- 

 impervious and more reliable methods of terminating E-M cables are needed. 



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