Fracture toughness of SmBaCuO bulk superconductors at cryogenic temperatures

Fracture toughness of Sm123 bulk superconductors with 16.7 and 28.6 mol% of Sm211 particles have been investigated by Vickers hardness test at cryogenic temperatures. The hardness test was carried out on [001] plane for two types of SmBCO bulk materials during 40-293 K. However, the hardness of Sm29 increased to 7,380 MPa with decreasing temperatures. In addition, fracture toughness of Sm17 and Sm29 are discussed calculating from Vickers hardness, median cracks length, Young's modulus and applied load. The fracture toughness of Sm17 became constant to 0.8 MPa/spl radic/m following the hardness property. The fracture toughness of Sm29 decreased from 0.73 Mpa/spl radic/m at 293 K to 0.67 Mpa/spl radic/m at 40 K.