Experimental Study Of Mechanical And Thermal Properties NbTi/Cu Superconducting Composite Wires At Cryogenic Temperature

Superconducting composites,which can sustain high carrying-current density if they reach superconducting state, are now available commercially for applications, in which they can generate the strong magnetic field. However, since the superconducting magnets were usually operated under complicated environments (cryogenic temperature and intense magnetic field). Based on a series of scientific and engineering questions (e.g. design and safe operation of superconducting magnets), the study of mechanical and thermal property of superconducting wires at cryogenic environment have become very important.Based on a ultra-low temperature mechanical properties test system,which were designed by Key Laboratory of Mechanics on Disaster and Environment in Western China, The Ministry of Education of China, Lanzhou University, this paper presents the effects of the variable cryogenic temperature on the tensile response for NbTi/Cu superconducting composite wires and its niobium-titanium filaments. At room tempreature and liquid nitrogen tempreature, the corresponding stress and strain relations are recorded during the wire stretched.Results show that tensile strengths,yield strengths and elongation of NbTi/Cu superconducting composite wires are increased with the decreasing of the temperature. NbTi filaments also have analogous behavior on its tensile strengths and elongation.And stress-strain curves of NbTi/Cu superconducting composite wires own obvious flexibility and strengthening phase;and the one of NbTi filaments only have flexibility phase. Sencondly, applying Multiphysics FEM packages of COMSOL,tensile behaviors of NbTi/Cu superconducting composite wire were also simulated.In addition, strain rate and holding time of immerse process dependences of mechanical properties of NbTi/Cu superconducting composite wire were discussed.To obtain comfortably thermal properties of NbTi/Cu superconducting composite wire,the method of stretch measuring of coefficient of linear expansion of wire was taken in this paper.The results show coefficient of linear expansion of NbTi/Cu wire have a strong cryogenic temperature dependence,and the relation between coefficient of linear expansion and cryogenic temperature show nonlinear.At cryogenic temperature,wires have showed negative thermal expansion properties.And by training of cryogenic temperature, coefficient of linear expansion of NbTi/Cu wire become more and more stable.