Modelling of local strain and stress relaxation in bronze processedNb3Sn wires

Abstract

Recently, the need for mechanical modelling ofNb3Sn wires has increased, since these wires are used in large projects such as the InternationalThermonuclear Experimental Reactor (ITER). The finite element method makes it possibleto solve multi-axial stress and strain distributions in complicated wire geometries. However,Nb3Sn conductors possess features that make building the mechanical model challenging andcomplicate the use of the finite element method. This paper focuses on two problems. First,detailed modelling of geometries with large filament amount can produce numericalproblems that are too large for computers. A simple approach to circumvent this problem ispresented, and its validity investigated. Second, the uncertainty in modelling thermalstress, caused by stress relaxation and other high-temperature phenomena, istreated. To investigate the credibility of the models, the computed results arecompared with critical current and stress–strain data measured for a bronze processedNb3Sn wire in an axial tension test. Computed results agree well withthe measured ones, and show that the mechanical strain state ofNb3Sn in filaments is very sensitive to the degree of stress relaxation.