The fretting fatigue crack propagation life prediction of Ti–6Al–4V by a two-stage dislocation-based model

Abstract

An accurate and rapid assessment of the fretting fatigue life of titanium alloys is essential for evaluating the structural integrity of aviation engine components. A two-stage fatigue crack propagation model for Microstructurally-Small Crack(MSC), Physically-Small Crack(PSC) and Long Crack(LC) was developed based on dislocation theory, incorporating cyclic plastic stress correction and crack closure effects. An averaging method was introduced to derive the microscopic parameters within the model, which was subsequently applied to fit fatigue crack propagation data (including short cracks, near-threshold long cracks, and steady-state long crack propagation) for Ti–6Al–4V. The results indicate that the deceleration effect exhibited by MSC at grain boundaries is a critical factor warranting attention. A fretting fatigue test was designed specifically for Ti–6Al–4V, with the contact stress field computed using finite element analysis. The elastic principal stress field at the contact edge can be categorized into three distinct regions based on varying stress characteristics. Fatigue cracks typically initiate in high-stress gradient areas near the contact edge and propagate inward under elevated shear stress within the transition zone. Utilizing this proposed model, predictions regarding Ti–6Al–4V’s fretting fatigue crack propagation life were made; these predictions closely align with experimental findings, predominantly falling within two standard deviations of the scatter band. These results demonstrate that MSC stage propagation significantly influences overall fatigue life under low-load conditions (approaching fatigue limits). This finding underscores our model’s robust explanatory and predictive capabilities concerning fretting fatigue life.