Notch fracture in gamma-titanium aluminides

The notch fracture behavior of two gamma-titanium aluminide alloys, having duplex and fully lamellar microstructures, has been investigated as a function of notch geometry and test temperature. The unnotched tensile properties and notch fracture loads are used to perform finite element analysis (FEA) to determine triaxial tensile stresses and effective plastic strains in the vicinity of notch roots. These results, together with fractographic examinations of notch failures, indicate that a crack nucleates in the triaxial tensile field when the effective von Mises stress just exceeds the uniaxial tensile yield stress. The high tensile stress component then propagates the nucleated microcrack to failure with local stress intensity reaching the toughness of the material. Thus, both plasticity and high tensile stress are required to cause notch failure.