Mechanical models for electrical cables

University dissertation from Stockholm : KTH

Abstract: A theoretical and experimental study of mechanical properties of electrical cables with multi order helical structure has been performed. Relations between applied deformations and local strains in the first order helical structure have been developed. The model is then generalized with a hierarchical approach where the strains at any order helical structure are expressed as functions of strains in the upper order helix under the assumption that all components are sticking to each other.The force balance between the strains and the friction forces is considered. When the cable is exposed to small bending curvature, the slippage of the component is prevented by the frictional force. At this stage, the components of the cable behave as solid beams. Slippage occurs between the components when the tensile force in the components overcomes the frictional force. This state occurs at sufficiently large bending curvatures and results in a variable bending stiffness varying with the magnitude of the applied bending curvature.The response of the cable to pure bending is measured and the data is evaluated using the theoretical model described above. Magnitudes of un- known properties of the cable are estimated by comparing the theoretical and experimental data. To utilize the model in terms of life time estimation, a number of parameters were suggested to relate the mechanical properties of the cable to wear and fatigue. A parametric study has been done to investigate how these parameters are affected by changing cable properties or the loading condition.