FATIGUE OF UNIDIRECTIONAL SCS-6 TI-24AL-11NB COMPOSITE CONTAINING A CIRCULAR HOLE/

Fatigue tests of notched unidirectional titanium aluminide composite, SCS-6/Ti-24Al-11Nb (at. pct), were performed to characterize the failu re modes and mechanisms that control the life of this material. Using middle-hole specimens tested over a range of stress levels, fatigue da mage was documented by optical photography, elastic compliance measure ments, and electrical potential drop measurements. It was found that a few dominant cracks form near the notch root and propagate into the c omposite matrix. Chemical removal of the matrix material and metallogr aphic sectioning of fatigue specimens examined prior to failure reveal ed that extensive fiber bridging of the matrix cracks dominated the fa tigue life. A detailed description of the failure modes and mechanisms of damage initiating in the vicinity of a circular hole is presented, and the relative roles of crack initiation and crack growth are discu ssed.