Optical fiber cable flexibility design under plastic deformation and its evaluation

Abstract

AbstractThis paper discusses the flexibility of a cable when it is bent to the range of plastic deformation of the cable material. Considering the situation where the cable material exhibits elastic or plastic deformation, the expression for the maximum bending moment, which represents the flexibility of the cable, is derived in terms of the following parameters: The strain‐hardening exponent n and the plastic modulus which are material parameters; and the outside and the inside radii r1 and r2, respectively, which are the structural parameters. As a method to determine the foregoing material parameters experimentally, the three‐point bending test is discussed. A method is presented which determines the strain‐hardening exponent n and the plastic modulus from the relation between the load P and flexion δ. The method is verified experimentally. The case is considered where the cable is composed of several materials such as sheath, core, and tension member, and it is demonstrated that the bending moment of the whole cable is given as a sum of the bending moments of the component materials. Thus, it is shown that if the material parameters of the cable components are known, the maximum bending moment of the whole cable, representing the flexibility, can easily be designed.