Fracture toughness evaluation of YBCO bulk superconductor

Evaluation of the fracture toughness of a Y-Ba-Cu-O bulk superconductor with 28.6 mol% Y-211 and 15 wt.% Ag has been investigated by tensile tests at room temperature using specimens with a sharp V-notch. The notch was introduced into the specimens such that its direction of depth was parallel or perpendicular to the c-axis and the loading direction was in the a(b)-axis. Fracture toughness evaluation by three-point bending tests was also carried out. In addition, usual tensile tests and three-point bending tests were also carried out in the specimens without V-notch. The scatter of measured fracture toughness values by the bending tests, 1.6-2.1 MPa m^1/2, was less as compared with that by the tensile tests, 1.1-2.5 MPa m^1/2. However, the average value in tensile tests 1.9 MPa m^1/2 coincided with that in bending tests. The maximum and the average value of bending strength, 109 and 104 MPa, were higher than those of tensile strength, 72 and 56 MPa, respectively.