Modified Modeling of Self-twist Process of Multistage Cable Based on Discrete Element Method
In the process of evaluating the mechanics properties of multi-stage twist cable, the accuracy of the cable model largely affects the prediction results. A self-twist modeling technology is proposed to apply to the discrete element model of multi-stage ca
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Abstract In the process of evaluating the mechanics properties of multi-stage twist cable, the accuracy of the cable model largely affects the prediction results. A self-twist modeling technology is proposed to apply to the discrete element model of multi-stage cable own to its advantage in dealing with large deformation of structures. The comparison between self-twist model and traditional theory model based on space configuration show that the self-twist model has an obvious superiority than theory model in the aspect of describing the microscopic contact and non-uniform pre-compressive stresses among the strands in the cable. The predictions of the stress-strain relationship using above two models show that space theory model is not applicable to the smaller pitch length and pitch ratios because of the too large void fraction and unrealistic contact force among strands, while the self-twist model has a much higher predicting precision from beginning to end. Keywords Multi-stage cable stress-strain relationship
Self-twist discrete dynamic model Axial tensile
1 Introduction Superconductor coils are assembled by huge amounts of ITER cable-in-conduit conductors (CICCs), and CICC consists of six petal sub-cables. The petal itself is composed of about 200 multi-stage twist strands and is compressed into the necessary configuration and void fraction [1]. In the actual operation environment, the current-carrying capability appears an unexpected degradation and even the superconducting performance will be lost due to strong transverse and axial deformation of strands [2]. Thus, the investigation of their mechanical properties is S.M. Jia D.M. Wang Lanzhou University, Lanzhou 730000, China X.J. Zheng (&) Xidian University, Xi’an 710071, China e-mail: [email protected] © Springer Science+Business Media Singapore 2017 X. Li et al. (eds.), Proceedings of the 7th International Conference on Discrete Element Methods, Springer Proceedings in Physics 188, DOI 10.1007/978-981-10-1926-5_123
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directly related to the operation stability and the structural safety of the ITER superconducting magnet system [3]. A great quantity of experimental studies demonstrated that the deformation of composite strand exhibits typical nonlinear plastic characteristic under axial tension [4], and the nonlinear effect of the sub-cable was enhanced with the increase of the twist stage [5]. However, the micro contact characteristics among strands are difficult to be probed by experimental methods due to the limitations of measurements. So some simplified mechanical models that aimed to estimate the mechanical properties of multi-stage cable were proposed. In 2005, the axial tensile stress-strain of superconducting strand based on the simple finite element model of three-layer structure was performed by Mitchell [6]. However, the nonlinear constitutive of inhomogeneous materials could not be described accurately as the unchanged mechanical parameters used in finite element program. In 2000, the prediction precision of th
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