Fracture toughness analysis of circumferentially-cracked around bars

The accuracy and the domain of applicability of approximate formulae used to evaluate the fracture toughness of circumferentially-Cracked Round Bars (CRBs) are established using finite element calculations. In the elastic plastic fracture mechanic (EPFM) domain, new formulae are developed which increase largely the accuracy and the domain of applicability. The loss of constraint is evaluated through the Q-factor allowing to determine the domain of validity of one-parameter fracture toughness characterisation. At the same time, an appropriate 'crack length to bar radius' ratio is proposed. A micromechanical model of cleavage fracture in the transition region is proposed where both the specimen size and loss of constraint correction are taken into account. This model allows to measure plane strain fracture toughness using small CRB.