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Two-step homogenization for the effective thermal conductivities of twisted multi-filamentary superconducting strand

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Applied Mathematics and Mechanics(English Edition) 2022年第5期43卷 689-708页

作者： Yongbin WANG Huadong YONG Youhe ZHOU Department of Mechanics and Engineering Sciences College of Civil Engineering and MechanicsLanzhou UniversityLanzhou 730000China Key Laboratory of Mechanics on Disaster and Environment in Western China Ministry of Education of ChinaLanzhou UniversityLanzhou 730000China

For the accurate prediction of the effective thermal conductivities of the twisted multi-filamentary superconducting strand,a two-step homogenization method is *** on the distribution of filaments,the superconducting strand can be decomposed into a set of concentric cylinder *** layer is a two-phase composite composed of the twisted filaments and copper *** the first step of homogenization,the representative volume element(RVE)based finite element(FE)homogenization method with the periodic boundary condition(PBC)is adopted to evaluate the effective thermal conductivities of each *** the second step of homogenization,the generalized self-consistent method is used to obtain the effective thermal conductivities of all the concentric cylinder *** accuracy of the developed model is validated by comparing with the local and full-field FE ***,the effects of the twist pitch on the effective thermal conductivities of twisted multi-filamentary superconducting strand are studied.

关键词： superconducting strand multi-filamentary two-step homogenization effective thermal conductivity

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Extraction on the Contact Forces Among the Opaque and Non-photoelastic Particles Under Electromagnetic Force

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Acta Mechanica Solida Sinica 2022年第2期35卷 248-260页

作者： Shuaike Jiao Cong Liu Jun Zhou Xingyi Zhang You-He Zhou Key Laboratory of Mechanics on Disaster and Environment in Western China Attached to the Ministry of Education of China Lanzhou UniversityLanzhou 730000China Department of Mechanics and Engineering Sciences College of Civil Engineering and MechanicsLanzhou UniversityLanzhou 730000China

Contact force is related to the mechanical response of superconducting strands under a large electromagnetic body force,which is important for the safety of the international t hermonuclear experimen tai reac tor(ITER)magne t struc *** to the complex st rue ture of the cable-in-conduit conductor(CICC),the component unit of the ITER magnet,and the extreme operating environment,the research on the strand contact force caused by the electromagnetic force has been progressing *** this study,a two-dimensional(2D)theoretical model based on the granular elemen t method is construe ted to compute the contac t forces among some opaque and non-photoelastic ferromagnetic particles which are placed in a non-uniform magnetic *** the experiment,the contact deformations of these particles may be obtained by the digital image correlation *** also propose a method,which is similar to the least-squares method,to calculate the electromagnetic body forces of different ***,the distributional and statistical characteristics of the contac t force chains and contact angles are presen *** is considered that the method proposed in this paper is suitable for the contact force analysis of the cross section of superconducting strands in the ITER CICC that is subjected to a transverse elec-tromagnetic *** the end,this 2D theoretical model is generalized to the three-dimensional(3D)case,and the concise mathematical framework is presented.

关键词： Contact force Electromagnetic force superconducting strand Cross section

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Critical Current and Fracture Behavior of Nb3Al superconducting strands under Cyclic Electromagnetic Force

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材料科学与工程（中英文版） 2011年第2期5卷 121-127页

作者： Yoshihide Wadayama Kyohei Natsume Toshiyuki Mito Shinji Hamaguchi Nagato Yanagi Kazuya Takahata Shinsaku Imagawa Department of Fusion Science School of Physical Science The Graduate University for Advanced Studies Toki-city Gifu 509-5292 Japan National Institute for Fusion Science Toki-city Gifu 509-5292 Japan

To obtain basic information on fracture behavior and its critical current properties in superconducting strands with long-term periodic excitation, a unique experiment of cyclic strain loading was carried out. The strain was applied to a superconducting filament directly at 4.2 K using an electromagnetic (Lorenz) force instead of the usual mechanical load. The sample strands were Jelly-roll process Nb3Al with a copper ratio of 2.1. A new magnet system to evaluate long-term cyclic strain loading was set up. It was able to generate external fields up to 14 T with 58 mm bore. Cyclic strain was applied by the sample current control: 500 A, 0.1 Hz. In the experiment, critical current measurements and applied cyclic strain were carried out in alternation and the variation of critical current was obtained during the cyclic test. In this paper, the experimental results of cyclic strain loading on the critical current of Nb3Al strand and mirostructural observation of fracture surface of the filaments is described. Our results show that degradation of critical current properties was not observed at cycle number n = 1500 under the applied axial strain of 0.17%. A noxious sample, from which the outside copper stabilizer was deliberately removed, broke after n = 10, and crack propagation was observed at the fracture surface of the Nb3Al filaments. Under a microstructural observation of the break sample, the fracture points of the filaments were seen to be different in a longitudinal direction. A striped pattern like a beach mark due to crack propagation was also observed at the Nb3Al fracture surface. It was found that the cross-sectional homogeneity of the strand is important to avoid the damage and breaking from cyclic loading.

关键词： superconducting strand mechanical strength Nb3Al jelly-roll cyclic strain microstructure

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