Modelling of local strain and stress relaxation in bronze processed Nb3Sn wires

Recently, the need for mechanical modelling of Nb(3)Sn wires has increased, since these wires are used in large projects such as the International Thermonuclear Experimental Reactor (ITER). The finite element method makes it possible to solve multi-axial stress and strain distributions in complicated wire geometries. However, Nb(3)Sn conductors possess features that make building the mechanical model challenging and complicate the use of the finite element method. This paper focuses on two problems. First, detailed modelling of geometries with large filament amount can produce numerical problems that are too large for computers. A simple approach to circumvent this problem is presented, and its validity investigated. Second, the uncertainty in modelling thermal stress, caused by stress relaxation and other high-temperature phenomena, is treated. To investigate the credibility of the models, the computed results are compared with critical current and stress-strain data measured for a bronze processed Nb(3)Sn wire in an axial tension test. Computed results agree well with the measured ones, and show that the mechanical strain state of Nb(3)Sn in filaments is very sensitive to the degree of stress relaxation.