Fracture behavior analysis of EuBaCuO superconducting ring bulk reinforced by a stainless steel ring during field-cooled magnetization

We have m agnetized the EuBaCuO ring bulk reinforced by a stainless steel ring during field-cooled magnetization (FCM) at 50 K under the magnetic fields from 6.3, 7.3 or 8.3 T, in which the ring bulk was broken at the intermediate step of FCM from 8.3 T. To discuss the fracture behavior of the bulk, we have performed the numerical simulation using a three dimensional finite element method for the bulk with realistic superconducting characteristics, and obtained both the electromagnetic hoop stress, sigma(FCM)(theta), during FCM and thermal hoop stress, sigma(cool)(theta), under cooling from 300 to 50 K. The difference of the thermal contraction coefficient between the bulk and the stainless steel ring caused an inhomogeneous sigma(cool)(theta) profile with a tensile stress at the outermost edge on the bulk surface under cooling process. The maximum of the total hoop stress, sqtotal(=sigma(FCM)(theta) + sigma(cool)(theta)), was estimated to be + 50 MPa and + 59 MPa during FCM from 7.3 T and 8.3 T, respectively. These results suggest that the actual fracture strength of the present ring bulk is between 50 and 59 MPa. The sigma(total)(theta) value should be reduced as low as possible in the whole area of the bulk to avoid the fracture behavior during FCM.