Fatigue Life Prediction Of Centrifugal Fan Blades In The Ventilation Cooling System Of High-speed-train

With the rapid development and maturity of high-speed train technology,high-speed train as a new means of transportation,with comfortable,convenient and efficient ride experience,has gradually become one of the most popular travel modes for the people.High speed train has the characteristics of high speed,long one-way mileage and short operation cycle interval,so how to ensure the safe and reliable operation of high-speed train is the key to the development of high-speed train technology.As the main heat dissipation device of traction motor,inverter and transformer system of high-speed train,the centrifugal fan blade of ventilation and cooling system of high-speed train play an important role in the safety performance of high-speed train.The centrifugal fan blades of the ventilation and cooling system of the high-speed train bear the interaction stress caused by the start and stop conditions of the fans for a long time,which is easy to cause the fan blades to fatigue failure,and may lead to accidents in the operation of the high-speed train.Therefore,it is of great significance to predict the life of centrifugal fan blades for high-speed train ventilation and cooling systems.To study the fatigue life of fan blades,a series of theoretical analysis and innovative tests were carried out.The main contents are as follows:?1?In this paper,by studying the fatigue load and life prediction method of the fan blade,a preliminary theoretical analysis was made on the load borne by the fan blade,and it was concluded that the main fatigue load borne by the fan includes centrifugal load,vibration and impact load and aerodynamic load.At the same time,systematically introduced the fan blade fatigue life prediction method and theory,by comparing the difference between the theory of fatigue analysis,and to build life prediction model based on the nominal stress,selection of power function form of S-N curve,Goodman linear model correction fatigue limit,Miner damage model to accumulate fatigue damage,and considering the fan structure of the effects of stress concentration on fatigue life.?2?Mechanical and fatigue properties of fan blade base material DC51D+Z were studied experimentally.The basic mechanical properties including yield strength,tensile strength,modulus of elasticity and elongation were determined by the static tensile sample of DC51D+Z material standard spline.Through DC51D+Z material standard spline stress ratio R=-1(R=₈4)9))/₈?6?)of axial tension and compression fatigue test,fitting the DC51D+Z S-N curve under symmetrical cyclic load,it was concluded that the fatigue limit is 195 Mpa,and by observing the fracture analysis of the samples after the test of the fatigue damage.?3?The finite element model of fan blade was established.The aerodynamic force of each blade of fan was analyzed by CFD numerical calculation method.The centrifugal force and vibration impact acceleration of fan blade were calculated by numerical calculation method.It was concluded that the static load of fan is mainly the centrifugal load caused by the start and stop condition of fan.To provide theoretical support for the real-time monitoring of the maximum stress point in the bench test,the maximum stress value and its distribution at the root of the fan blade were analyzed by simulating the actual start and stop conditions of the fan with the finite element method.A modified method for predicting the fatigue life of centrifugal fan blades in the cooling and ventilation system of high-speed trains based on the nominal stress method was proposed.Based on the nominal stress,the total damage was calculated by using the S-N curve and Miner cumulative damage rule.The fatigue life of fan blades was predicted to be 6.9 years by the model.?4?In this study,the accuracy of the prediction model was verified through the fatigue test of the fan blade bench.Based on the high-speed slip-ring induction method,the fan blade fatigue bench and dynamic stress data measurement system were built.The fatigue bench system could be adjustable with frequency conversion,and the stress state at the dangerous point of the high-speed rotating fan blade could be monitored in real time.After the fatigue test,the fracture of fan blade was observed by scanning electron microscope?SEM?,and it was determined that the fatigue failure of blade root was caused by the crack initiation,and the crack propagation caused the blade fatigue failure.Finally,a comparison was made between the test data and the prediction model data.The results showed that the relative error between the test data and the prediction model was 18.1%,indicating a good correlation between the two,which verified the practicability and validity of the prediction model.Therefore,the research results could prevent fan blade faults in advance,and lower the probability of fan blade damage accidents,and improve the reliability of the ventilation and cooling system of high-speed train.This research has a good theoretical and practical significance,completed the construction of the life prediction model of the fan blade,built the fatigue bench system of the fan blade,verified the accuracy of the model by comparing the data of the test and prediction model,and provided a reference for the life prediction of the fan in the ventilation and cooling system of the typical high-speed train.