Modelling, simulation and experimental investigation of cables

• Applicants: Professor Dr.-Ing. Stefan Diebels; Professor Dr.-Ing. Alexander Düster
• Subject Area: Mechanics
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405490285

Cables are complex systems that consist of various components and are versatile enough to be used, for example, in automobiles or in industry robots. The composition of the cable thereby influences its mechanical properties significantly. The interaction between the components or layers of a cable results not only in energy dissipation due to friction but also influences the stiffness in various loading directions. In the first project part it was found that an elasto-plastic anisotropic material model in combination with fully 3d high-order hexahedral elements is appropriate for modelling thin beam like structures exhibiting an anisotropic behaviour. However, for a complex cross section such as for coaxial cables, the anisotropy is not sufficient to describe the interaction between the layers in bending situations. The interaction can be seen in tensile tests as the stick-slip effect, where an oscillation of the tensile force can be observed. Moreover, the reproducibility of the bending tests was reduced, which could be attributed to the different orientation of the conductors in the cable.The aim of the continuation proposal is to study the effect of the interaction between the individual layers. To this end tensile, torsion and bending tests will be conducted on self-assembled cables and industrial cables. The experiments will be conducted hierarchically at each level of the assembly. In a similar way an industrial cable will be hierarchically disassembled and tested at each stage of disassembly. Moreover, a new sample holder will be constructed such that the relative motion between the layers is fixed.In the first project part the reproducibility of the results could be increased significantly with the help of initial tensile loads. This will be analysed systematically in a study of the initial loading regarding its type and amplitude.To model the behaviour the cross-section of the cable will be discretised layer by layer. On each layer a separate material model with individual parameters will be applied. On the one hand the strong anisotropy arising in the layers containing the conductors is represented by the anisotropic material model, while on the other hand the protective jacket will be represented with an isotropic elasto-plastic material model. The parameters will be identified similarly to the experimental tests in hierarchic fashion.Another aim of the continuation proposal is to study the effect of friction when the outer surface of the cable is in contact with an object. It will be experimentally examined by gliding the cable tangentially against a contact partner for varying surfaces. To improve the efficiency of the mortar method describing the contact, an adaptive moment fitting scheme is used for the integration of the contact forces. Further, the representation of locally arising plasticity is improved by implementing and investigating the interpolation of the history data for adaptive hp-refinement.

• DFG Programme: Research Grants