Direct Measurement on the Residual Stress in $$\hbox {YBa}_2\hbox {Cu}_3\hbox {O}_{7\text {-}\updelta }$$ YBa 2 Cu
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ISSN 1860-2134
Direct Measurement on the Residual Stress in YBa2Cu3O7- δ Bulk Superconductors Fabricated by Top-Seed Melt-Textured Method Xianglin Zhang1
Suming Qiu1 Yulong Wang1 Jun Zhou1,2 1,2 Xingyi Zhang Youhe Zhou1,2
Xiyang Su1,2
(1 Department of Mechanics and Engineering Sciences, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou 730000, China) (2 Key Laboratory of Mechanics on Disaster and Environment in Western China Attached to the Ministry of Education of China, Lanzhou University, Lanzhou 730000, China)
Received 3 July 2020; revision received 25 August 2020; Accepted 1 September 2020 c The Chinese Society of Theoretical and Applied Mechanics 2020
ABSTRACT The residual stress is formed in YBa2 Cu3 O7- δ (YBCO) bulk superconductors, which undergoes a complex fabrication process and experienced a huge temperature change about 1000◦ C. The residual stress may result in micro-cracks in YBCO bulks and cause degradation of its superconducting and mechanical properties. It will be greatly helpful to reform the structural designs if the distribution of residual stress in YBCO bulk can be investigated. The traditional method of measuring residual stress does not apply to oxide ceramics as they are brittle materials. In this paper, a YBCO bulk was sliced into pieces of several millimeters in height, which could thus be treated as a plane-stress problem. The residual stress and principal stress angle for YBCO bulk have been obtained by an artificial hole-drilling method with very low speed.
1. Introduction The study of residual stress can not only provide guidance for the microscopic preparation process of materials, but also be correlated with the safety design of macroscopic applications of materials, especially for ceramic superconducting materials. YBa2 Cu3 O7- δ (YBCO) bulk superconductors are widely used in the magnetic levitation system [1–3], superconducting permanent magnet [4, 5], and vibration dampers [6, 7], due to their excellent levitation force and magnetic freezing capacity. The solid-state sintered technique [8], top-seed melt-textured growth (TSMTG) [9], and top-seeded infiltration and growth (TSIG) [10] are mostly used in the fabrication process of YBCO bulk at present. The YBCO bulk experiences a compaction process before sintering, which causes pre-stress. There are different types of phases, such as the YBa2 Cu3 O7 /Y2 BaCuO5 /Ba3 Cu5 O8 (Y123/Y211/ Y035) phases in the TSIG [10], the Y123/Y211 phases in the TSMTG [11], and the Y123 phase in the solid-state sintered technique. Stresses appear during fabrication because of the different expansion coefficients of Y211, Y123 and Y035 phases and the dependence of Y123 phase lattice parameters on the oxygen stoichiometry [11]. The TSMTG and TSIG processes bring more residual stress than the solid-state sintered process for YBCO bulks. The huge residual stress may result in micro-cracks in YBCO bulks, cause degradation of its superconducting and mechanical properties and shorten its
Corresponding author. E-mail: zhangxingy
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