The Role of Laser Shock Processing Treatment in the Growth Dynamics of Fatigue Cracks in Specimens of Ti-6Al−4V Titanium Alloys Damaged by Foreign Objects

Foreign object damage (FOD) is one of the main factors reducing the service life of wings, engine blades, aircraft compressors, and highly loaded machine components. This article presents a detailed study of the peculiarities of the growth rates of fatigue cracks upon FOD in the vicinity of the leading edge of a Ti-6Al−4V titanium alloy blade exposed to preliminary laser shock processing treatment. The FOD and the laser shock processing treatment were modeled using 3D numerical analysis by the finite-element method. The resulting range of changes in the effective stress intensity ratios takes into account both the fields of residual stresses caused by FOD and the crack closure effect due to residual compression stresses. The derived effective stress intensity ratios are used to analyze the growth rates of fatigue cracks in complex residual stress fields. Such actual operational loading modes are considered as low-cycle and multicycle fatigue, separately and in combination.