Thermal-electromagnetic Coupling Fracture Mechanics Analysis Of High Temperature Superconductors

High temperature superconductors have higher critical temperature,higher critical current density and can capture larger magnetic fields.These excellent material properties make them widely used in the preparation of superconducting magnets and cables.The large-scale application requires the ability to work in complex environments without failure.During the use of superconducting materials,thermal stress,electromagnetic force,and other mechanical stresses may cause the micro-cracks existing in the manufacturing process to propagate and eventually cause fracture.The ability of the superconducting materials to carry current will be greatly affected.Considering the temperature rise during the magnetization process and the fluctuation of the coolant temperature under the capture field,the thermal stress and electromagnetic force will change accordingly.The fracture performance of superconducting structures will be affected by temperature changes.When studying this thermo-electromagnetic coupling fracture problem,a quasi-static superconducting critical state model that does not consider t he effect of temperature on the critical current density is no longer applicable.This dissertation will study the thermo-electromagnetic coupling fracture of superconducting materials based on a generalized superconducting critical state model that considers the relationship between temperature,magnetic field and current.This dissertation firstly considers the single-layer superconductor as the research object.The unidirectional coupling of temperature to current is considered in the study,which makes the temperature change cause the change of electromagnetic force.The results show that the peak of the stress intensity factor(SIF)during the pulsed field magnetization will occur when the temperature rises.The higher the temperature rises,the higher the peak value.A superconducting layer with substrates is established based on the model in first part.We consider the obstruction to thermal conduction.At this time,the temperature is unidirectionally coupled to the force and the current,and the temperature change will change the thermal stress and electromagnetic force inside the superconductor.The study compared the thermal and magnetic stresses in the structure.The results show that the thermal SIF dominates the initial stage of heat conduction,and the magneto-induced SIF dominates the late stage.In addition,the SIF during field cooling magnetization and zero field cooling magnetization decreases as the thickness and Young's modulus of the substrate increases.However,the thermal SIF during heat conduction increases as the thickness and modulus of elasticity of the substrate increases.Double cantilever beam(DCB)is the main experimental model for studying fracture problems.At the end of this paper,a theoretical model of DCB based on cohesive theory is established to explore the peel force-displacement curve under different magnetic fields.The results show that the crack of DCB is easy to propagate under the action of the open electromagnetic force.The DCB with small crack has good adaptability to the oscillation of the magnetic field,and that with larger crack is more likely to fracture when the magnetic field drops.In addition,the finite element results show that the error of theoretical model is small.