Research On High Cycle Fatigue Characteristics And Prediction Method Of TC17 Titanium Alloy Blade Damaged By Foreign Objects

During the take-off,landing and low-altitude cruising of the aero engine,small hard objects such as gravel in the environment,screws and nuts,and metal debris will be sucked into the engine inlet along with the high-speed air flow,impact and damage engine blades.Due to the centrifugal force,aerodynamic force and vibration load when the fan / compressor rotor blade is working,fatigue cracks may be generated and expanded at the damaged blade,or even lead to blade fracture,endangering flight safety.This not only reduces the remaining service life of the fan / compressor blade,but also causes accidents such as blade breaking and flying out,damaging the casing and other blades,and endangering flight Security.Therefore,the research on the law of blade damage by foreign objects is carried out to further analyze the influence of damage on high cycle fatigue performance,and improve the prediction accuracy of high cycle fatigue limit of foreign object damaged blade.It has important economic and engineering application value for the design of fan / compressor blade resistance to foreign object damage and the maintenance and repair problems in the process of field use.In this paper,the damage mechanism of the fan / compressor rotor blade is studied,the influence of high cycle fatigue and the research status and progress of fatigue prediction methods for fan /compressor rotor blade are investigated and summarized.Theoretical analysis and experimental research are carried out on TC17 titanium alloy rotor blade for foreign object damage and fatigue prediction.The main works are as follows:(1)Carry out static and dynamic mechanical performance tests of TC17 materials,the real stress-strain mechanical properties of the material were obtained,and fit the TC17 J-C model constitutive equations.Through numerical simulation to calculate the modal of the TC17 compressor blades,to obtain the stress distribution under different vibration modes,and the dangerous position of the leading edge is determined according to the stress distribution as a simulated foreign object impact position.The process of the steel ball impacting the leading edge of the blade under different working conditions is numerically calculated to analyze the influence of foreign object impact parameters on the damage law.The 2mm and 3mm steel balls were used to impact the leading edge of the blade from different angles(0°,30°,45°,60° and 90°)at a speed of 250m/s.It was found that with the increase of impact angle,the notch edge would form a tear damage containing material loss,forming a large stress concentration.(2)The air gun method was used to test the leading edge of flat and curved blades under various damage parameters.According to the test data of the flat blade,the influence of the impact test parameters(foreign object size,foreign object type,foreign object shape,incident angle,leading edge radius,impact velocity)on the geometric parameters of the damage notch was analyzed.The step-by-step method was used to conduct high cycle fatigue test on the bending simulation blade damaged by foreign objects,and the influence of various parameters on the fatigue limit of notched bending simulation blade was studied.The microstructure of fatigue fracture surface was observed by scanning electron microscope(SEM),and the law of fatigue crack initiation was analyzed.With the same impact angle,the larger the size of the steel ball,the higher the impact velocity,and the greater the damage depth.With the increase of the damage depth,the fatigue limit presents an obvious downward trend.The microcosmic characteristic analysis of high cycle fatigue fracture shows that the larger the impact Angle is,the more obvious the material dislocation will be.(3)The node displacement method is used to calculate the stress intensity factor at the notch under different damage parameters(notch angle,notch radius,crack radius),and the effect of the damage parameter on the stress intensity factor was analyzed.The Peterson formula in the average stress model was employed to predict the high cycle fatigue limit of the curved simulated blade,and the accuracy of the prediction model was discussed by comparing with the experimental results.Based on the influence law of notch angle,notch radius and crack radius on stress intensity factor,the Peterson formula was modified for the two parameters of damage angle and crack radius,and the improvement of prediction accuracy of fatigue limit of foreign object damaged blade was discussed.(4)The modified Peterson model is verified with real compressor rotor blades.For the real TC17 titanium alloy blade,the foreign object damage test and high cycle fatigue test were also carried out.The modified Peterson model was used to predict the fatigue limit of the real blade notch.The accuracy of the prediction model in the application of the real blade was analyzed by comparing with the test results.The modified fatigue limit prediction model proposed in this paper has been verified to be of high accuracy.It provides a more convenient means for solving the current design of aero-engine fan /compressor blade resistance to foreign object damage,and provides a more convenient means for the field maintenance and repair of aero-engine foreign object damaged blade.