科研之友
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摘要
An inner annular crack in an infinitely long superconducting cylinder is modeled, and its fracture properties under electromagnetic forces are investigated. First, the flux density distributions in the superconducting cylinder of the present crack model are obtained analytically for both zero-field cooling (ZFC) and field cooling (FC) activation processes, where the magnetically impermeable crack surface condition and the Bean model outside the crack influence region are adopted. Then the stress intensity factors (SIFs) at both inner and outer crack fronts are calculated by the finite element method (FEM). Some important phenomena are observed. Among others, in the process of field ascent, the state corresponding to the applied maximal magnetic field is the most critical. In the process of field descent, for the FC case, the crack always propagates and grows from the inner crack front, and it is easier to propagate when the crack is close to the cylinder's center. For the ZFC case, although the crack generally propagates from the inner crack front as well, whether the crack would propagate or not depends on the crack position, crack size and the applied field. The crack is generally easier to propagate for the FC process than for the ZFC process. The findings from this study are very useful for detailed analysis and design of superconducting materials.
