
Prof. Peifeng Gao
Lanzhou University, China
Title: Mechanical failure and electromechanical degradation of high-temperature superconducting composite tapes under extreme conditions
Abstract:
High temperature superconducting (HTS) conductors, represented by Rare Earth-Barium-Copper-Oxide (REBCO) coated conductor (CC) tapes, are promising for high energy and high field superconducting applications. Due to layered composite materials consisting of multiple laminated high-aspect-ratio (HAR) layers with vastly different material properties, and a complex preparation process, REBCO CC tapes exhibit mechanical sensitivity under extreme operating environments. As a result, it is difficult for traditional mechanical modelling and analysis methods to reveal the properties such as thermal stress mismatch, mechanical failure of interlayer delamination and electromechanical degradation at ultra-low temperatures. To effectively solve the difficulty of mesh delineation and calculation of REBCO CC tapes in three-dimensional (3D) FE models, and to construct the real structure of the conductors as much as possible, mixed-dimensional modeling methodology for general laminated composites with HAR thin films is developed for elastic-plastic deformation and interfacial delamination analyses. The major thin constituent layers, namely, the silver, REBCO and buffer layers, are modeled as two-dimensional (2D) surfaces while the relatively thick stabilizer and substrate are in 3D layers. All the adjacent layers are coupled via spring equations. First, the thermal residual stresses and strains accumulated during the fabrication and cooling processes are analyzed by a multi-step modeling method that emulates the manufacturing process. Then, with the residual stresses and strains as initial stresses and strains, the mechanical behavior under a tensile load is studied. Under the framework cohesive zone model, a mixed-dimensional delamination model is further developed. The model includes all the major constituent layers of a typical REBCO and is experimentally validated at both the conductor and constituent-layer levels. In addition, verification through a full-3D FE counterpart model shows that the mixed-dimensional model performs simulations with much higher computational efficiency than the full-3D counterpart while maintaining sufficient accuracy. Further, a general predictive model based on the strain dependence of the Weibull distribution function of statistical damage of superconducting filaments is developed to explore the influence of the uniaxial, bending, torsional and combined deformation modes on critical current degradation, and the model predictions are in good agreement with the experimental structure.
Keywords: mixed-dimensional; laminated composites; delamination; thermal mismatch; finite element model; cohesive zone model; electromechanical degradation
Biography:
Sep 2013-Jun 2017
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Ph.D. in Engineering, College of Civil Engineering and Mechanics,
Lanzhou University, Lanzhou, China
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Nov 2015-Dec 2016
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Doctoral Research Student at Department of Material Science and Engineering,
North Carolina State University, USA
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Sep 2010-Jun 2013
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M.E. in Engineering, College of Civil Engineering and Mechanics,
Lanzhou University, Lanzhou, China
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