ABSTRACT

The large flexural-torsional behaviour of a cable is investigated both analytically and experimentally in a three dimensional Cartesian coordinate system. The cable is assumed to be subject to arbitrary terminal moments, where the bending moments are anti-symmetric and the twisting moments are symmetric. The cable is idealised as an elastic beam with uniform circular cross-section, whose axial and torsional stiffnesses are coupled. Transverse displacements of both· ends of the cable are prevented while the longitudinal displacement is allowed. The rotations of the ends with respect to the principal transverse axes are caused naturally by the applied terminal moments. Experiments are carried out on both an elastomeric rod and a cable. The three dimensional deflected configurations are produced in the experiments corresponding to the specified end constraints. The consistency between analytical prediction and experimental measurements is presented.

INTRODUCTION

It is well known that a straight elastic beam will deform into a out of plane configuration when it is subject to the combined action of terminal bending and twisting moments. This phenomenon can be readily observed if one experiments with a length of household electrical lead or garden hose. The distorted configuration is usually accompanied by large deformations and it is easy to form various kinds of two dimensional loops. When this happens to a marine cable, a kink or bird caged section will most likely be observed after the cable is re-straightened by the application of tension. Kinks or bird caged sections can lead to severe damage of the cable structure and the internal conductors. In this paper, the large three dimensional nonlinear elastic deformation of the cable is investigated both analytically and experimentally, where the cable is assumed to be purely subject to terminal bending and twisting moments.

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