环氧树脂固化工艺条件对YBCO超导带材临界电流的影响

为了研究固化条件对超导带材临界电流的影响,采用电测法实验测量了多种固化工艺条件下YBCO高温超导带材的临界电流。分析得到热处理温度140℃时,超导带临界电流出现明显退化,温度越高退化越明显;超导带临界电流随着固化时间的延长而降低,处理温度越高,随时间下降的幅度越大,并从超导体钉扎效应的角度对实验结果进行了初步的分析。     

YBCO超导带材研究进展

简要回顾了高温超导带材的发展历史,然后系统地总结了YBCO超导带材的构成、基带、过渡层和超导层的制备方法,并介绍了当前国内外的研究水平和新近取得的进展,尤其是国内最近的重要进展.在此基础之上,对YBCO超导带材的应用和市场前景进行了展望.     

铁磁性基底对第二代高温超导带材交流损耗的影响

对采用不同工艺制备的不同基底的第二代高温超导带材的交流损耗进行了测量,并研究了铁磁性基底对其交流损耗的影响。结果表明,电流较小时,具有铁磁性基底的带材损耗要远大于Norris临界态模型计算值,并且制备工艺的不同也会对带材交流损耗产生一定影响。考虑铁磁基底的铁磁损耗,将铁磁损耗和磁滞损耗进行相加后,实验测量值和Norris模型很好地吻合,说明铁磁基底高温超导带材的损耗具有很大的影响。实验研究结果表明,对于采用PLD工艺制备的YBCO超导带材,基底没有磁性,带材交流损耗不受铁磁损耗影响,而采用IBAD工艺制备的哈氏合金基底YBCO带材和采用RABiTS工艺制备的Ni-W基底YBCO带材,由于基底具有磁性,在通电电流较小时,带材交流损耗不仅要考虑超导体的磁滞损耗,还要考虑基底铁磁损耗的影响。     

实用化高温超导材料研发进展

综述了目前国内外实用化高温超导材料研发的最新进展,系统介绍和总结了Bi-2223、YBCO涂层导体、MgB2线带材和YBCO块材等主要的实用化高温超导材料制备和性能的最新结果.对比了美国、日本和韩国等国家的高温超导材料研发模式,分析了实用化高温超导材料的发展趋势及应用前景.     

高温超导线圈绕制工艺及性能测试研究

针对高温超导用Bi系高温超导带材,对其在77 K自场下和应变疲劳下的临界电流进行了测试。介绍了超导限流器用大型高温超导线圈及绕制工艺,在77 K自场下对比研究了双饼线圈、螺线管线圈的V-I特性曲线;通过反复试验得到了最佳接头焊接工艺,满足了磁体稳定工作的条件。结果表明:当弯曲次数小于或等于10次时,高温超导带材的临近电流不受径向弯曲次数影响;绕制的高温超导线圈性能良好,77 K自场下的临界电流为168.12 A,当焊接温度达到493 K、搭接长度4 cm、焊料Sn_(63)Pb时焊接效果最佳。     

拉应力作用下YBCO涂层导体的交流损耗

YBCO涂层导体长带将逐步应用于各种强电领域,如电缆、变压器、超导电机等.YBCO带材在应用过程中,不可避免会受到各种机械应力的作用,这些应力很可能会对YBCO涂层导体的临界电流密度、交流损耗等物理性能产生影响,从而限制其实际工程应用.     

Bi2223/Ag高温超导带材失超传播特性研究

对高温超导Bi2223/Ag带材在自场、气冷环境条件下的失超传播速度进行了实验研究,并比较分析了不同传输电流条件下带材失超的最小触发能量。实验结果表明:Bi2223/Ag高温超导带材的失超传播速度范围在0.1—0.6 cm/s,其失超传播速度与传输电流大小有关,与触发能量无关,带材载流越大,失超传播越快;存在最小传输电流48.5 A,带材失超传播在该电流值以下被截止。     

应用高温超导线(带)的研制现状与进展

提供了当前高温超导线的最新发展,第一代高温超导材料的机电性能参数和热物性参数,以及4种美国超导公司的商业产品和中国超导带材的基本参数.论述了第二代高温超导线的研究进展.从高温超导电力应用的观点,展望高温超导电力技术应用前景,文中的工程与实验数据对高温超导线(带)材的应用可供参考.     

YBCO超导带材二次冲击恢复过程的模拟及实验研究

YBCO超导带材失超后的快速恢复对于电阻型超导故障限流器(RSFCL)重合闸应对二次故障电流冲击至关重要.当前研究通常将电阻恢复视为带材恢复,在实际的盘式结构中存在复杂的微孔结构,一次冲击恢复至超导态时仍存在大量气泡滞留,影响带材的二次冲击恢复过程.针对典型的微孔结构建立了三维模型,采用CFD模拟并结合大电流冲击实验,...     

各种平均应力下高周疲劳极限间的定量关系

疲劳极限是材料工程应用中的一个重要特性参数,但它并不是材料常数。在不同循环载荷作用下,材料会有不同的疲劳极限值。疲劳极限值很大程度上依赖于循环载荷中的平均应力或最大应力幅值,两者之间的关系是材料自身固有的特性关系。因为在接近疲劳极限的低循环应力幅下,S-N曲线受疲劳极限控制,所以在工程应用中对其定量关系有迫切的需求,但现有的经典经验关系只能对其进行非常粗略的估算,不能满足工程应用中有关寿命设计的需要。现状是只能通过大量的实验,得出其实验关系。该文提出了一种函数形式的关系式,该关系式可以足够精确地描述各种材料的疲劳极限和平均应力之间的关系,且只包含三个材料常数。只要这三个材料疲劳特性常数被事先确定,则任意疲劳载荷下的疲劳极限值,都可由该关系式估计得到,因此可以作为材料本身固有的疲劳强度的状态关系式使用。     

Characterization of Multi-field Behaviors on Fatigue Damage Due to High Cyclic Loading in YBCO-Coated Conductors Fabricated by the IBAD-PLD Technology

In practice, yttrium barium copper oxide (YBCO) tapes often experience different types of fatigue loadings including continuous winding stress, repeated thermal cycles, and periodic electromagnetic force, consequently resulting in a poor performance. Based on cyclic loading tests in the structural design of some large YBCO superconducting devices, a 95% critical current (I_c) retention tensile stress criterion was proposed. Although the relationship between critical current and stress/strain has been extensively studied by some research teams, the effects of fatigue loading on macro-behavior, microstructure, and electromechanical responses have not been much reported. In this paper, the tapes were made using ion-beam-assisted deposition combined with pulsed laser deposition. Under the self-field, they were subjected to many cycles of axial loading to test their fatigue behavior. In this work, first, we report the effects of fatigue numbers on YBCO tapes’ tensile responses (e.g., Tensile Strengths) and electromechanical behaviors. Macro-behavior measurements showed that the mechanical behaviors and their electromechanical degradation of YBCO superconducting tapes depended on the number of fatigue loading cycles. Then, fracture surface morphologies of YBCO tapes’ superconducting layer and Hastelloy layer were also investigated with scanning electron microscope and energy-dispersive X-ray spectroscopy. It was found that the width of scratch lines and the size of fatigue defects on Hastelloy layer were increased with the number of fatigue cycles, which was the main cause of the degradation of mechanical properties. Moreover, observations of the microstructure conducted on the YBCO layer demonstrated that it was the crack motion and evolution that led to the current degradation under fatigue loading. During the process of fatigue loading, the small fatigue cracks become big with the increasing fatigue number. Lastly, a critical current-strain model of the fatigued HTS tapes, that combines the Ekin power-law formula and the Weibull distribution function, is proposed. This model can predict the electromechanical property of fatigued YBCO tapes under uniaxial tensile strain well.

     

1991 12th International Conference on Magnet Technology

The following topics are dealt with: accelerator magnets; fusion magnets; superconducting motors and generators; MHD (magnetohydrodynamic) magnets; high magnetic fields, wigglers, undulators, and test facilities; NMR (nuclear magnetic resonance) magnets; magnetic separation; instrumentation and measurements; stability and AC losses; materials; computations; cryogenic systems and components; and magnets and conduit conductors     

The Contradiction Behavior Between Mechanical Performance and Degradation Mechanism of Electric at Cryogenic Temperature in Bi-2222/Ag Tapes with Different Protective Layer

The mechanical performance at cryogenic temperature and the degradation mechanism of electric behaviors of Bi-2222/Ag tapes with different protective layers as well as their contradiction laws are discussed. A variable temperature cryostat system is constructed to provide the successive cooling environment from room temperature (RT) to the liquid nitrogen temperature (LNT), and a cryogenic-type extensometer is also used to measure strain behavior of the superconducting tapes. And, the effects of bending strain on the critical current of Bi-2222/Ag tapes with different protective layer were measured using arched abrasives with different radius. Experimented results have shown that the protective layer of the tapes could have strong positive effects on the measured mechanical performance at room temperature and cryogenic temperature. The irreversible degradation on strain indicates that the I _c reduction is caused mainly by crack formation and propagation in the brittle Bi-2222/Ag tapes. In particular, the degradation mechanism of multifilamentary sample with protective layer was also elaborated, and protective layer has some negative effect on electric behaviors. In addition, the behaviors of the n value with strains on standard Bi2222/Ag tape was also argued to predict the damage process in Bi-2222 tapes indirectly during bending tests.     

A review of mechanical behaviour and stress effects in hard superconductors

The mechanical properties of type II superconducting materials are reviewed as well as the effect of stress on the superconducting properties of these materials. The bcc alloys Nb-Ti and Nb-Zr exhibit good strength and extensive ductility at room temperature. Mechanical tests on these alloys at 4.2 K revealed serrated stress-strain curves, non-linear elastic effects, and reduced ductility. The non-linear behaviour is probably due to twinning and de-twinning or a reversible stress-induced martensitic transformation. The brittle A-15 compound superconductors, such as Nb₃Sn and V₃ Ga, exhibit unusual elastic properties and structural instabilities at cryogenic temperatures. p]Multifilamentary composites consisting of superconducting filaments in a normal metal matrix are normally used for superconducting devices. The mechanical properties of alloy and compound composites, tapes, as well as composites of niobium carbonitride chemically vapour deposited on high strength carbon fibres are presented. Hysteretic stress-strain behaviour in the metal matrix composites produces significant heat generation, an effect which may lead to degradation in performance of high field magnets. Measurements of the critical current density, J_c, under stress in a magnetic field are reported. Modest stress-reversible degradation in J_c is observed in Nb-Ti composites while more serious degradation is found in Nb₃Sn sample.The importance of mechanical behaviour on device performance is discussed.     

Research on Bitter-like HTS Magnet Energized by Flux Pump with Single Thermal Switch

Journal of Superconductivity and Novel Magnetism - High-temperature superconducting (HTS) tapes are gradually developed in superconducting magnets with a high magnetic field with commercialization...     

低温工程领域的新机遇

简要介绍和讨论了低温工程领域3个令人兴奋的进展。首先描述了提高电-燃气轮机混合驱动飞机性能的两个机会:采用超导电机或定子实现超过30kW/kg的推重比,或者使用含液化天然气的混合燃料。第二个机遇是基于氢燃料电池汽车,扼要给出了氢燃料电池汽车在商业部门的快速发展情况,液氢的供应和运输是氢燃料电池汽车相关基础设施的重要组成部分。第三探讨了小型等离子体热核反应装置的新兴发展情况,等离子体热核反应将在未来10到15年成为人类重要的清洁能源来源。由于小型等离子体热核反应装置依赖于工作在超高磁场强度的高温超导磁体,所以它将为低温工程领域带来一系列创新的机会。     

A lightweight low-current 10 K magnet for space-flight ADRs

Future space missions will include detectors and other components cooled to cryogenic temperatures by adiabatic demagnetization refrigerators (ADRs) coupled with mechanical cryocoolers. In such systems the ADRs require lightweight, low-current superconducting magnets. At least one of an ADR’s magnets must operate at the cryocooler’s coldest stage temperature. This temperature should be as high as possible in order to improve operating efficiency and design flexibility. Until now all space-flight compatible magnets have been made with NbTi wire, which has limited their operating temperatures to below about 5 K. We have developed a lightweight (1 Kg) low-current (8 A) Nb₃Sn magnet which produces a 3 T central field at 10 K. We explain the choice of this magnet’s specifications and describe its performance testing.     

Mechanical and transport properties of IBAD/EDDC–SmBCO coated conductor tapes during fatigue loading

In electrical devices like superconducting motor, generator and SMES, HTS coated conductor (CC) tapes will be subjected to alternating stress or strain during manufacturing and operation. The repeated loading will affect the mechanical integrity and eventually the electrical transport property of CC tapes. Therefore in such applications, electro-mechanical property of CC tapes should be evaluated. In this study, the endurance of an IBAD/EDDC–SmBCO CC tape under high-cycle fatigue loading has been evaluated. Applied maximum stress and fatigue life (S–N) relation was obtained at 77 K. The mechanical properties and the critical current, I_c, of the sample under fatigue loading were investigated at 77 K. Considering the practical operating environment, the effect of the stress ratio R, on the degradation behavior of I_c under fatigue loading was also examined.     

Low-temperature tensile strength of the ITER-TF model coil insulation system after reactor irradiation

The windings of the superconducting magnet coils for the ITER-FEAT fusion device are affected by high mechanical stresses at cryogenic temperatures and by a radiation environment, which impose certain constraints especially on the insulating materials. A glass fiber reinforced plastic (GFRP) laminate, which consists of Kapton/R-glass-fiber reinforcement tapes, vacuum-impregnated in a DGEBA epoxy system, was used for the European toroidal field model coil turn insulation of ITER. In order to assess its mechanical properties under the actual operating conditions of ITER-FEAT, cryogenic (77 K) static tensile tests and tension-tension fatigue measurements were done before and after irradiation to a fast neutron fluence of 1×10²² m⁻² (E>0.1 MeV), i.e. the ITER-FEAT design fluence level. We find that the mechanical strength and the fracture behavior of this GFRP are strongly influenced by the winding direction of the tape and by the radiation induced delamination process. In addition, the composite swells by 3%, forming bubbles inside the laminate, and loses weight (1.4%) at the design fluence.     

Effect of substrate thickness on interfacial adhesive strength and thermal residual stress of second-generation high-temperature superconducting tape using peel test modeling

Second-generation high-temperature superconducting (2G HTS) tape is used in magnets and cables because of its outstanding electromagnetic characteristics. However, with the development of winding technology, thinner tapes are required in the construction of magnets. The effect of using thinner substrates on the resulting mechanical and electrical properties of 2G HTS tapes must thus be urgently understood. The interfacial adhesive strength is an important index used to characterize the mechanical strength of 2G HTS tape. Previous experimental studies have shown that thermal stress is one of the major factors in the delamination of the component tape used for magnet winding or cable assembly. In this study, the effect of substrate thickness on the interfacial adhesive strength of 2G HTS tape was investigated using peel test modeling. The thermal residual stresses accumulated during tape synthesis and caused by altered temperature during tape preparation and application at 77 K were also considered. To address the geometrical, physical, and boundary nonlinear problem, the finite element method was used. The simulation results indicate that interfacial stress caused by thermal shrinkage may separate the tape near the superconductor layer at the outer edge; however, no significant effect was observed for the central part. When the thermal residual stress was considered, the peel strength was reduced by approximately 20%. The substrate thickness also played an important role in the magnitude of thermal residual stress, which resulted in an increase of the peel strength with decreasing substrate thickness.