Influence of foreign object damage on the high cycle fatigue tolerance of gas turbine aerofoils under complex loading

Vibratory loading at high frequencies can lead to catastrophic failure in rotating engine components because of the very high number of HCF cycles which can be encountered in very short times, therefore it is imperative to remain below the stress conditions corresponding to the onset of crack growth due to HCF. The HCF threshold and crack growth onset conditions from simulated FOD, representative of service induced damage, as compared with sharp precracks, will be determined for a titanium alloy representative of those used in aero-engine aerofoils.This will be carried out under combined HCF/ LCF Iloading and ultimately under simulated flight cycle conditions. The FOD will be typical of that encountered in service and characterised in terms of its geometry, size, residual stress field and microstructural modification. The fundamental mechanisms of crack growth involved from FOD, as compared with sharp pre-cracks, will be determined using microscopy and fractography. Fatigue life predictive models will be assessed and developed for both pre-cracks and FOD under complex loading.