Abstract:
A phenomenological model has been developed to predict the remaining useful life of flaw-damaged Ti-6Al-4V Beta-STOA titanium and 7075-T73 aluminum rotorcraft components. The model extends the use of traditional notched fatigue analysis methods that were developed for machined notches, down to the scale of small surface flaws such as dents, dings, scratches, gouges and corrosion pits. The highly stressed volume in the vicinity of flaws is used for reference in the model calibration. This eliminates the requirement to define an equivalent notch root radius for an arbitrary flaw shape. Calibration of the model was performed using sets of dogbone fatigue coupons with embedded surface flaws. Validation of the model was performed using other sets of dogbone and double-edge notched tension (DENT) flawed coupon fatigue test data, under both constant-amplitude and spectrum loading. Validation results have shown that the model provides reasonably accurate life predictions within the range of calibration of the model, when compared to a reference S-N working curve. The analytical capability demonstrated here has important implications for current life management practices of rotorcraft dynamic components. Fatigue life prediction of flaw damaged components is a key enabling technology for the application of Condition Based Maintenance (CBM) practices to rotor system structures.