NOTCH FRACTURE IN GAMMA-TITANIUM ALUMINIDES

The notch fracture behavior of two gamma-titanium aluminide alloys, ha ving duplex and fully lamellar microstructures, has been investigated as a function of notch geometry and test temperature. The unnotched te nsile properties and notch fracture loads are used to perform finite e lement analysis (FEA) to determine triaxial tensile stresses and effec tive plastic strains in the vicinity of notch roots. These results, to gether with fractographic examinations of notch failures, indicate tha t a crack nucleates in the triaxial tensile field when the effective v on Mises stress just exceeds the uniaxial tensile yield stress. The hi gh tensile stress component then propagates the nucleated microcrack t o failure with local stress intensity reaching the toughness of the ma terial. Thus, both plasticity and high tensile stress are required to cause notch failure.