Micromechanical aspects of crack-length effect on fracture toughness and transition behaviour in steels

Cast C-Mn steel predetermined for container casks of spent nuclear fuel has been tested extensively from the point of view of resistance against brittle fracture. For the fracture toughness evaluation the three-point bend specimens with different crack length (varying a/W approximate to 0.5; 0.21 0.1) and with the same ligament below the crack tip have been used. Shift of transition regions and temperatures up to lower temperatures with lower crack length values has been determined. Higher average values of fracture toughness and higher scatter in fracture toughness values were obtained when testing specimens at the same temperature. Stress distributions below crack tip have been calculated by finite element method (ABAQUS code) for each specimen geometry separately. Modification has been introduced into calculation taking into account specific material behaviour. The J-Q curve has been obtained from the experimental data set tested at temperature -100degreesC.