Research On Damage Characteristics And Simulation Test Of Foreign Object Damage Of Blade

In the near-ground operation state, aircraft engine inhales a variety of high-speed hard foreignobjects with the high-speed flow, such as small stone, gravel, rivets etc., which will produce theimpact damage to fan/compressor blade. The impact damage caused by hard foreign objects is called"foreign object damage"(FOD for short). FOD has four basic characteristics: stress concentration atthe damage; residual stress field near the damage; small cracks at the damage area; micro-structuraldamage at the damage. In the high-cycle fatigue loading, FOD can easily induce the initiation andrapid expansion of fatigue crack, causing the blade fatigue fracture failure, thus becoming a seriousthreat to flight safety. Therefore, it is of great practical significance to investigate the blade FOD toreduce and avoid accidents as much as possible and to ensure the safety of the engine and aircraftflight.The investigations and analysis of the characterization and tests simulation of FOD were carriedout by three aspects as follows:(1) The macro and micro damage characteristics of FOD are analyzed and summarized based onscrapped28fan blades. It shows that the main forms of damage are pits and notches (including nicksand piece out). For notches wider than0.5mm, they are usually in a range of0.5~2.5mm width and0~1.0mm depth and concentrates in the middle of leading edge and trailing edge. The SEM photos ofnotches demonstrate that the typical micro-features are plastic deformation, micro notches, microcracks and lamellar structure.(2)21FOD was simulated on TC4plate specimens by using self-designed gas gun test system,and then HCF fatigue strength of damaged specimens was determined by tests. It is obtained thatsimulated FOD is presented with typical macro and micro blade FOD characteristics. The fatigue testsof damaged specimens indicate that FOD definitely weakens the fatigue strength of specimens. Thefatigue fractures of the damaged specimens reveal that the FOD provides favorable conditions for thefatigue crack initiation and expansion.(3) Numerical simulation of blade FOD was studied by using LS-DYNA and Johnson-Cookmaterial model where the characteristics of residual stress around FOD are analyzed. Studies haveshown that the FEM model established in this paper, which is used for FOD numerical simulation, iseffective in a certain scope of precision. According to the results of FOD numerical simulation, thereare obvious tensile and compressive residual stress zones around the FOD. With comparison of fatigue fractures of damaged specimens, it indicated that great tensile residual stress caused by FOD isone of the important factors leading to fatigue failure of the damaged specimens.