Owing to its excellent superconducting properties and well-developed fabrication processes, Nb 3 Sn has become a key material for 10-16 T high-field superconducting magnet applications. However, the Lorentz forces and thermal stress during operation may lead to crack initiation and propagation in the epoxy matrix, thereby affecting the magnet stability. In this study, samples were extracted from Nb 3 Sn superconducting magnets and subjected to tensile, compressive, and shear tests at room temperature and 77 K. The corresponding crack initiation and propagation behaviors were subsequently characterized. The average tensile fracture strength increased from 13.35 MPa at room temperature to 25.72 MPa at 77 K. Similarly, the compressive strength rose from 139.61 MPa to 266.25 MPa, and the shear strength from 38.93 MPa to 71.80 MPa. In addition, finite element simulations were performed to replicate the mechanical experiments of the Nb 3 Sn samples. The zero-thickness cohesive elements were embedded within the epoxy matrix. The stress concentration was analyzed to elucidate that the epoxy region within the stress concentration area served as the site for crack initiation and propagation. Tensile crack propagated perpendicular to the loading direction, while compressive cracks intersected at specific angle. Shear cracks extend from the high-stress concentration point to the bottom of the convex-shaped sample. The simulation results were in good agreement with the experimental data, thereby validating the proposed model.
Bi et al. (Wed,) studied this question.