Grain boundary deformation in uniaxial strained Nb3Sn

We generated a three-dimensional stress map of grains and grain boundaries in uniaxial strained Nb3Sn composite, using a scale-coupled model generated by the polycrystalline finite element method and based on the linear elastic theory of closely packed fiber-reinforced composites. The model takes into account the transfer of stress from a Cu-Sn matrix to a single Nb3Sn filament composed of inner elongated and outer equiaxed grains. Due to differences in grain morphology and orientation, stress inhomogeneity arises first in the filament. The interconnected grain boundary networks in Nb3Sn constrain grain deformation by fostering stress concentration at intersections between multiple grains. The degree of stress concentration can be as high as 2.08. Our model simulations show a random distribution of grain boundary orientations within stress concentration zones and provide detailed information on how and where stress inhomogeneity is likely to produce crack initiation in Nb3Sn.