Simulation studies of mechanical stresses in REBaCuO superconducting ring bulks with infinite and finite height reinforced by metal ring during field-cooled magnetization

We have performed the numerical simulation of mechanical stresses (hoop stress, σ _θ and radial stress, σ _r) in REBaCuO ring bulks with an infinite and finite height reinforced by metal (aluminum alloy or stainless steel) ring during field-cooled magnetization (FCM) using a solenoid coil with an infinite and finite height. The superconducting characteristics of the bulk material were assumed to follow Bean's critical state model. The electromagnetic hoop stress, ${{\sigma }_{\theta }}^{FCM},$ of the finite height ring bulk during FCM using the infinite coil was larger than that for the infinite ring bulk, and the time step dependence of ${{\sigma }_{\theta }}^{FCM}$ was clearly different in each case. The ${{\sigma }_{\theta }}^{FCM}$ value was reduced by the reinforcement by the metal ring, and the stainless steel ring was more effective than the aluminum alloy ring. The ${{\sigma }_{\theta }}^{FCM}$ value of the finite ring bulk magnetized using the finite coil was slightly reduced, compared to magnetization using the infinite coil. The thermal hoop stress, ${{\sigma }_{\theta }}^{cool},$ which occurs in the ring bulk when cooling down to operating temperature due to the difference of thermal contraction coefficient between ring bulk and metal ring, was also estimated. The compressive, ${{\sigma }_{\theta }}^{cool}$, was reduced comparatively at the uppermost surface of the ring bulk because of the larger thermal contraction of the metal ring along the axial direction. The actual total hoop stress, ${\sigma }_{\theta }(={{\sigma }_{\theta }}^{FCM}+{{\sigma }_{\theta }}^{cool})$ was analyzed for the finite ring bulk reinforced by the metal ring during FCM and the possibility of mechanical fracture due to this hoop stress is also discussed. (paper)