Fracture toughness of Sm123 bulk superconductors evaluated by tensile and bending tests

The effects of test temperature and Sm211 (Sm₂BaCuO₅) secondary phase particles on the fracture toughness of the Sm123 (SmBa₂Cu₃O_x) single grain bulk superconductors were investigated by tensile and bending tests using the V-notched specimens. The correlation between the obtained fracture toughness by tensile and bending test was not necessarily good. The fracture toughness obtained by the indentation method was lower than them. The tensile fracture toughness for the crack propagation in the c-axis, 1.2-1.3 MPa m¹2/, was higher than that in the direction perpendicular to the c-axis, 1.0-1.1 MPa m¹2/. Although the former increased with increase in the Sm211 molar fraction, the latter did not increase. There was no appreciable difference between the fracture toughness obtained by the tensile tests at LNT and that at RT, while the fracture toughness from the indentation method at LNT was slightly lower than that at RT.