Tensile Behavior Analysis of the Nb 3Sn Superconducting Strand With Damage of the Filaments

The complex structure of the superconducting strand and different mechanical and thermal properties of the component materials make its mechanical behavior difficult to be predicted well, and some experimental phenomena are hard to explain, for example, the “platform” in the stress-strain curve of the powder-in-tube (SMI-PIT) strand. Thus, developing better numerical models is very necessary. In this paper, taking the SMI-PIT strand and internal tin (LMI) strand as examples, their stress-strain characteristics under tensile load at different temperatures are simulated with finite-element method models. In these models, the complex internal structure, the initial thermal residual stress, and the damage of the filament and its evolution are taken into consideration. The “platform” in the stress-strain curve of the SMI-PIT strand is explained commendably, the relevant influence factors about this “platform” are discussed, and the reason why this “platform” does not occur in the curve of the LMI strand is also explained. From the discussion, we find that the distribution of the break points in the filaments will affect the slope of this “platform,” and the initial crack decides the start point of the platform. The calculated results agree well with the experimental data.