Effect of a single overload on the cyclic R-curve behaviour of a γ-TiAl TNM alloy

The effect of single overloads on the threshold of stress intensity range of a semi-brittle material, a γ-titanium aluminide, was analysed. This material class exhibits a pronounced R-curve behaviour, which is mainly caused by the formation of shear ligaments, crack deflection and branching. Samples with short cracks on deep sharp notches were subjected to overloads of 80 % of the fracture toughness. Contrary to ductile materials, the experiments revealed no significant increase in the long-crack threshold, however a pronounced increase in the slope of the R-curve for the threshold of stress intensity range.