A damage mechanics-based fatigue life prediction method for TC4 components considering combined influence of scratch defects and structural geometric features

Aircraft structural components may suffer surface scratches during manufacturing or service. In this study, fatigue tests were conducted on TC4 titanium alloy specimens with scratch defects to investigate the influence of scratch depth on fatigue life. Based on continuum damage mechanics and the fatigue damage evolution law of scratch-free materials, an equivalent fatigue damage model was developed, which incorporates the effect of surface scratches while avoiding complex finite element simulations and significantly reducing computational effort. To account for the combined influence of scratch defects and local geometric features, the model was further enhanced by incorporating stress gradient effects and multiaxial equivalent stress. Multiaxial fatigue tests on open-section scratched TC4 titanium alloy tubes were conducted to validate the enhanced model, and the predicted results show good agreement with the experimental data. The methodology enables direct fatigue life estimation of scratched components based on stress analysis of scratch-free counterparts, eliminating the need for complex local stress field analysis around scratches and demonstrating significant advantages for engineering applications.