When the deformation behavior of both fiber and matrix is ductile in composite materials, ductile fibers exhibit uniform elongation or multiple necking depending on their volume fraction in matrix. In the present study, deformation behavior of Nb-Ti filaments in Nb-Ti/Cu superconducting composite wire was investigated using finite element analysis. Large displacement elastic-plastic analysis was carried out for monofilament composites of volume fraction of filament (V_f) of 0.14 to 1.0. Slight reduction of diameter was given to the filament to initiate necking. Multiple necking was observed for composites whose V_f was less than 0.3. The interval of multiple necking was also investigated by placing several initiation points on the filament in the analysis. The results showed that the interval of the multiple necking was about three. These results agreed well with the experimental observation for Nb-Ti/Cu and W/Cu composites.
