Low Temperature Mechanical Properties of RE-Ba-Cu-O Large Single-Grain Bulk 150 mm in Diameter

Evaluations on the mechanical properties such as fracture strength and fracture toughness were carried out at 77 K for an RE-Ba-Cu-O (RE: rare-earth elements) large single-grain superconducting bulk 150 mm in diameter through bending tests for specimens cut from the bulk. The average fracture strength value of the large single-grain bulk at 77 K was slightly higher than that at room temperature. While an inner region of the bulk has pores, a region near the top surface of the bulk has few pores. The maximum fracture strength value was obtained for a specimen cut from the low-porosity region near the top surface. While the porosity of the large single-grain bulk and that of a smaller single-grain bulk are similar to each other, the average fracture strength value at 77 K of the former bulk was lower than that of the latter bulk. The lower fracture strength of the large single-grain bulk corresponded to the lower fracture toughness.