Investigations Of Mechanical And Electrical Behaviors In Bi2212 Multi-filaments Superconducting Wire

High temperature superconducting materials have high critical temperature,critical magnetic field and critical current.It has shown huge potential in many fields such as energy,transportation,medical treatment and scientific research,which has been one of the hot topics in the application of superconductivity.Because of the excellent superconductivity and unique material structure,Bi₂Sr₂Ca₁Cu₂O_8+x?Bi2212?has become a candidate for engineering application.Bi2212superconducting composite wire is composed of Bi2212 filaments,Ag and high strength alloy sheath.Bi2212 is a kind of ceramic material which has poor toughness.Cracks often appear in the wire under mechanical load so that the critical current can be degraded.There are many voids and inclusions due to the limitation of fabrication method,which leads to the serious degradation of the critical current under the action of the strain.Then,the superconductivity of Bi2212 is very sensitive with the percentage of constituents.This paper focuses on the mechanical and electrical properties of Bi2212 wire.The critical current density,the tensile strength and the curves of stress-strain have been discussed based on the theoretical model.After combining with some numerical results,some valuable suggestions on the wire optimization can be provided.The degradation of critical current in Bi2212 composite wire under compression load is considered in the second chapter.The Bi2212 wire could be considered as a unidirectional filament-reinforced composites for the theoretical analysis.By considering the influence of inclusion and residual strain,the microbuckling wavelength can be deduced with the two dimensional model.Based on the experimental results,the critical current is fitted as a function of buckling wavelength.Then,the change of microbuckling wavelength with material parameters is discussed.Finally,the critical strain in the wire with filament bridge is analyzed using finite element method.The tensile strength of multifilament superconducting wire is considered in the third chapter.The filament failure and failure stability are considered in this study.By using hierarchical model and considering the load transfer and stability,the failure probability of Bi2212 wire under tension load can be obtained.It can be found that the size effect and the shear strength of matrix can influence the failure of filament bundle.The reliability and critical current of Bi2212 wire is studied in the fourth chapter.Current distribution at the defect can be derived by the basic electrical theories.Because of the many similarities between the shunting behavior of superconductor and the fracture of brittle material,the model we used in the third chapter is also available in this study.The failure probability of Bi2212wire under current load can be obtained.It can be found from the result that the critical current of Bi2212 wire is also influenced by size effect.Some material parameters and reasonability are also discussed in this chapter.The stress-strain behavior of Bi2212 wire under tension load is studied in the fifth chapter.By considering the single filament strength as a stochastic variable,a finite long filament bundle semi-analytical method is established.Using this model,the failure process of filament bundle structure can be obtained.Then,the stress-strain relationship can be analyzed.The numerical results match well with the experimental results.