The position dependence of fracture behavior in a superconductor/ferromagnetic bilayer strip

The effect of crack position and length on the fracture behavior in the superconductor/ferromagnetic (SC/FM) bilayer strip is investigated with finite element method. Owing to the composite structure of the SC/FM hybrids, the electromagnetic body force acting on the SC/FM bilayer strip will lead to complicated mechanical deformation during magnetization. The crack is prone to propagate even in the field ascent stage when the crack gets close to the sample bottom, which is quite different from the feature in a single SC sample. Moreover, the crack length and position leads to two inverse variations of stress intensity factor (SIF). SIF is positive and has peak value in the intermediate stage of field reduction when crack is close to superconducting layer. By contrast, SIF is positive except the intermediate stage and has maximum value at the beginning of the descent stage. Such novel behavior of SIF versus applied field can be explained by the strain distribution along the thickness direction for various crack positions. Generally, the maximum SIF at the maximum applied field is much larger than that in the field descent stage. The fracture behavior at the upper tip and lower tip exhibits significantly different characteristics. The maximum SIF at the lower tip is much larger than that at the upper tip as the crack is sufficiently close to the bottom surface.