Computational estimates of stress intensity factors for cracks in conductor jackets in a bonded winding

A single rectangular conductor jacket, including the surrounding insulation, has been modelled using finite element computational techniques. Such jackets are typical of the situation in a force flow cooled superconducting coil, where the jacket encloses the current carrying cable and the liquid helium coolant. Elliptical shaped cracks in the jacket have been included in the model to evaluate the stress intensity factors at the crack tip for three crack sizes at three different locations. Results using 3D finite elements are presented for a typical semi-elliptical surface crack in a single conductor jacket under tensile loading. It has been found that mesh and element sizes contribute to the variation in the values of the stress intensity factors calculated but that the relative accuracy of the results is generally within ±5%.