II. MECHANICAL PROPERTIES, MATERIALS, AND CONFIGURATIONS 

 OF LOAD-CARRYING COMPONENTS 



Background 



E-M cables can be purchased off the shelf from a number of manufac- 

 turers. » The construction of such cables usually consists of (1) 

 centrally located conductors (coaxial or multiple pairs); (2) a layer of 

 insulation; and (3) two contrahelically-wound layers of steel armor. 

 Often these off-the-shelf cables do not meet requirements of the user 

 and, as a result, most cables are purchased on special order; specified, 

 designed, and fabricated for a particular purpose. An example of such 

 a cable is shown in Figure II-l. 



In reviewing cable failures, it was found that many problems arose 

 out of five causes : 



1. User did not know what cable was needed to provide 

 proper performance; 



2. User applied cable to a purpose for which it was 

 not originally intended; 



3. Manufacturer bid for and attempted to make the 

 cable beyond his technical abilities; 



4. Manufacturer made the cable from incomplete 

 specifications or without knowing the intended 

 purpose; and 



5. Manufacturer and user never tested sample of the 



cable to see if it met all of the design specifications. 



There are areas of E-M cable technology that need improvement, parti- 

 cularly in the types of material used as the load-carrying member and the 

 configuration of such members within the cable design. The resulting 

 mechanical properties and behavior that are exhibited by the armoring 

 and load-carrying members of the cable are also areas that need further 

 research. 



Materials 



The materials that have been used as strength members in E-M cables 

 are shown in Table II-l. Other materials^ that can be used as load- 

 carrying members and armor include low carbon steel, plow steel, extra 

 plow steel, copper-covered steel, cadmium bronze, and beryllium copper. 

 These other types of material are suggested for use in special environ- 

 mental, magnetic, weight, strength, or other requirements. 



The material-^ most commonly used as a strength member is galvanized 

 improved plow steel. The tensile strength of this material varies with 

 the wire diameter as shown in Figure II-2. Variations in the tensile 

 strength for a given diameter occur because of differences in actual 

 diameter and slight variations in the manufacturing process. The dashed 

 line represents the average tensile strength and is used for design 

 purposes. For comparison purposes, Figure II-3 shows the tensile strength 

 properties of stainless steel wire types. 



The primary advantage of steel is the large strength-to-diameter 



