Research On Influence Of Foreign Object Damage On Stainless Steel Blade High Cycle Fatigue Property

When the aircraft taking off,landing or flying at low altitude,the engine will inevitably inhale into the sand,stone and metal objects such as bolts with high speed airflow.This will cause foreign object damage(FOD)to the fan / compressor blades.Under the action of high cycle vibration load,blade cracks and expanding will easily caused by foreign object damage,also the fatigue performance of the blade will be reduced.Therefore,it is significantly important to research the influence of foreign object damage on engine blades high cycle fatigue strength and master the prediction method of fatigue strength of FOD blades.The main research conclusions of this paper are as follows:(1)Simulation blade with leading edge was designed according to the leading edge size characteristics of the blade features section of a stainless steel compressor.Foreign object damage simulation tests of simulation and real blades were carried out on cannon gun test system.The macro and micro damage of notches was observed to obtain micro characteristics of notches caused by cannon gun method.FOD can be divided into smooth area,material accumulation and loss area.Microscopic characteristics include shearing band,shearing dimple,plastic deformation,micro crack and so on.(2)High cycle bending fatigue tests of standard test specimens,damaged simulation and real blades were carried out by step method on vibration table to obtain fatigue limits of each specimen.The results show that the damage types(shapes)affect the fatigue limit of specimens obviously.And the smaller damage depth,the greater fatigue limit.On the premise of the similar FOD size,the fatigue limit of simulation blade is about 30% lower than the real blade.The microscopic observation of fatigue fracture was proceeded to find that the internal defect caused by FOD is the main cause of the fatigue crack source producing at the notch.(3)According to the size and appearance of notches,the prediction of the fatigue limit was carried out based on average stress model.The average stress model is simple in form and convenient in calculation.However,the prediction results show that the prediction error of bending fatigue limit is large and aggressive.The prediction error of tearing and V-type notches is higher than semi-circular and scratching notches.The prediction method of the average stress model is revised based on the experimental results in this paper.The revised prediction results have a greater improvement than the previous ones.The research in this paper on the prediction method of fatigue limit of simulated blade and real blade can provide reference for the tolerance design of engine fan / compressor blade,and also provide a basis for the maintenance criterion of FOD blade,which is of great engineering significance.