Research On The Effect Of Thermal Stress On Crack Growth In High-Temperature Cylinderical Superconductor

High temperature superconductors(HTSs)have received extensive attention and research because of its great practical value.In order to get a better application for HTSs in practice,HTSs have many important mechanical properties worth studying besides its various basic features.Due to a necessary process of cooling in operation of HTSs,in this paper,the distribution of the thermal stress and strain in the process of zero field cooling(ZFC)is studied based on the mechanism of thermodynamics in elastic mechanics.At the same time,because the crack for the preparation and application of superconductors have an important impact,and as an inevitable problem of the study of the mechanical nature is also studied.Firstly,the heat conduction equation of cylindrical superconductor that is cooled in liquid nitrogen is solved by analytical method and the exact distribution of the temperature field is obtained.The temperature of the superconductor decreases rapidly in a short time at the initial time,and then slowly,until it tends to the temperature of liquid nitrogen.At the same time,the superconductor has a large temperature difference in different positions along the radial direction.Secondly,based on the research method of thermal stress in elastic mechanics,the distribution of the thermal stress and strain in the superconductor model is studied for different material parameters,and the results of three kinds of material parameters are compared.When the elastic modulus is constant,both the radial stress and hoop stress of superconductor is increased first and then decreased,while the maximum of radial stress and hoop stress appear in the center of cylinder,the difference is that the radial stress is always tensile stress,and the value of hoop stress at the center of cylinder is positive,and it is negative at the edge of cylinder.The radial and hoop strain are increased with the time,and the closer to the edge changes faster.When the elastic modulus is exponentially related to the position coordinate,the radial stress,hoop stress,radial strain and hoop strain are similar to the previous case,and the difference is that the maximum of radial stress appear in the middle position of the radius.For the case of the thermal expansion coefficient changing withtemperature,it is very close to the case that the elastic modulus is constant.Finally,the relationship between the stress intensity factor at the crack tip and temperature and the crack length is investigated by using the stress method in the conditions of zero field cooling.The stress intensity factor first increases and then declines with time.And the larger difference of temperature between the inside and the outside of the superconductor,the greater the value of the thermal stress intensity factor.Meanwhile,the stress intensity factor increases with the increase of the crack size,and the temperature and crack size have an important effect on the thermal stress intensity factor.