Initial damage influence of stiffness reduction for bronze route Nb3Sn strands

Nb3Sn strands are widely used in ITER CICCs, and the axial stiffness reduction induced by the initial damage in the form of filament breakage during processing of the composite strand is intensively related to the operation performance criteria. In this paper, an analytical model is developed to simulate this degradation of bronze route strands. The model contains three sub-models: the effective modulus of a filament with initial damage is investigated by a shear-lag model based on the global load sharing scheme and Weibull fiber strength statistics; the weakened stiffness of the superconducting layer is deduced by the Mori–Tanaka model; and the effective axial modulus of the strand is obtained by the multilayered generalized self-consistent model. The results indicate that the stiffness reduction of a strand presents obvious nonlinear behavior and depends on the initial damage parameter and the evolution of total damage.

► An analytical model is developed to describe the axial stiffness weakening by the initial damage.
► The stiffness reduction is obviously nonlinear.
► The model can be used to validate other numerical methods.