Development And Experimental Research Of High-temperature Ultra-high-frequency Fatigue In-situ Test Apparatus Under Complex Loads

The rotor blades of aircraft engine are the key components that determine the performance of the engine,and they are subject to extremely harsh service conditions: the huge centrifugal force resulting from high-speed rotation,the bending and torsional loads caused by the highspeed airflow,the high-frequency vibration caused by the aerodynamic factors and mechanical reasons,the high-temperature environment caused by fuel combustion,as well as the wet and hot environment,and corrosive environment.At present,it has become a hot issue for engineers to correctly evaluate the very-high-cycle fatigue behavior of blade materials under extreme conditions and complex conditions.However,the development of such work is severely restricted due to the lack of dedicated test apparatus and testing methods.Therefore,it is of great significance to develop dedicated very-high-cycle fatigue testing apparatus and testing methods to evaluate the very-high-cycle fatigue behavior of blade materials under extreme conditions and complex conditions,to safeguard the safety of aircraft engine operation,guide the selection of materials,structure design and manufacturing of new generation blades.The paper systematically investigates the existing complex condition very-high-cycle fatigue testing technology,and analyzes the coupling effect of high-temperature and complex loads on the mechanical properties of materials from a theoretical perspective.On this basis,a hightemperature ultra-high-frequency fatigue in-situ test apparatus under complex loads is developed.Based on the self-developed apparatus,the static and dynamic behavior research of typical aeroengine blade material under high-temperature and complex loading,as well as the very-high-cycle bending fatigue behavior research are carried out.The main research work of this paper is as follows:(1)The theoretical research of material mechanics performance test under high-temperature and complex static-dynamic load.Up to now,the coupling influence rule of composite deformation and bending vibration of blade material under high-temperature and complex load has not been fully understood.In this context,this paper carries out the theoretical research of material mechanics performance test under high-temperature and complex static-dynamic load.The composite deformation theory of one-dimensional homogeneous beam under the combination of high-temperature tension-bending was deduced,and the coupling influence rule of high temperature,tension and bending on the composite deformation of one-dimensional elastic beam was analyzed.The dynamic test theory of cantilever beam under the combination of high temperature tension-bending was deduced,and the influence of high-temperature environment and axial tension on the first-order and second-order bending vibration frequency of one-dimensional elastic beam was studied.(2)Development of high-temperature ultra-high-frequency fatigue in-situ test apparatus under complex loads.In response to the major needs of very-high-cycle fatigue test under extreme environment and complex conditions of aero-engine blade material,this paper conducts a functional analysis and framework design of the apparatus,develops the modules of static-dynamic mechanical loading,ultra-high frequency loading,temperature loading,in-situ monitoring,data acquisition and control,and so on.The integration and debugging of the whole apparatus and calibration are carried out,forming the high-temperature ultra-high-frequency fatigue in-situ test apparatus under complex loads with stable and reliable performance.Various module performance tests and characteristic function verification tests are conducted to verify the reliability and applicability of the apparatus.(3)Experimental study on the static behavior of typical aero-engine blade materials under high-temperature and complex loading.Based on the self-made apparatus,this paper carries out experimental study of the static mechanical behavior of typical aero-engine blade materials TC4 alloy and Inconel 718 alloy under high-temperature and complex loading.The coupling effect rules of high-temperature,tension and bending on the composite deformation behavior of TC4 alloy and Inconel 718 alloy were revealed.The combined tension-bending performance of equiaxed,bimodal and Widmanstatten structures of TC4 alloy were systematically compared.In addition,the coupling effects of high-temperature,tension and bending on the elastic-plastic mechanical behavior and failure mechanism of bimodal structured TC4 alloy were revealed.(4)Experimental study of very-high-cycle bending fatigue behavior of typical aero-engine blade materials under complex loading.Based on the self-made apparatus,an experimental study on the very-high-cycle bending fatigue behavior of typical aero-engine blade materials TC4 alloy and Inconel 718 alloy under complex loading was carried out.The effect of axial tension load on the fatigue behavior of TC4 alloy and Inconel 718 alloy in very-high-cycle bending was investigated,and the stress-life relationship of the materials under combined tension-bending was derived.In addition,based on Weibull’s theory,the prediction model of very-high-cycle fatigue life of materials under combined tension-bending was initially established,and the coupling effect law of tension and bending on the very-high-cycle fatigue life of materials was revealed from the theoretical point of view.This article is aimed at the major requirements of aviation engine blade material service performance testing,and overcomes the key technologies of composite static and dynamic mechanical loads,continuous temperature change of high and low temperatures,complex static and dynamic force-thermal coupling,etc.A performance stable and reliable high-temperature ultra-high-frequency fatigue in-situ test apparatus under complex loads is developed.The apparatus provides an innovative technical means for the performance testing of aviation engine blade materials under extreme environment and complex conditions,and has a wide range of applications in the testing of key components and materials in the fields of aviation,aerospace,nuclear industry,automobile,rail transportation,etc.