涡扇发动机高压压气机叶片裂纹萌生及扩展寿命预测研究

发布时间：2018-07-03 01:51

本文选题：涡扇发动机 + 高压压气机叶片　；参考：《天津大学》2015年博士论文

【摘要】：高压压气机叶片是涡扇发动机的关键转动件,其可靠性直接影响发动机性能和飞行安全。在发动机服役期间,疲劳断裂是高压压气机叶片的主要失效形式,裂纹在交变载荷作用下逐步萌生并扩展。若叶片在工作过程中发生疲劳断裂,除了影响发动机性能外,高速脱离的碎片将对整个转子系统及机匣造成严重的二次损伤,研究高压压气机叶片的疲劳裂纹萌生和扩展问题对提高航空发动机可靠性有着重要意义。叶片寿命评估贯穿于发动机设计、制造、使用以及维修整个全寿命周期,因此,考虑航空发动机工况复杂多变的特点,建立准确的高压压气机叶片疲劳寿命预测模型具有重要的科学意义和工程应用价值。Ti 6Al 4V钛合金以其优异的中高温力学性能成为高压压气机叶片的主要制造材料,本文采取叶片材料疲劳试验和模拟仿真相结合的方式,对高压压气机叶片裂纹萌生及扩展寿命进行研究预测,主要内容包括:进行Ti 6Al 4V钛合金叶片模拟试件振动疲劳试验,包括恒幅加载、变幅加载和裂纹扩展试验,分析变幅载荷应力差、循环比等参数变化对变幅加载下叶片疲劳寿命的影响。研究叶片的裂纹萌生及扩展规律,利用超景深显微镜和扫描电子显微镜观测疲劳断口微观特征,进一步探讨应力比、过载、高低周复合加载等变幅加载因素对叶片裂纹扩展速率的影响。基于Haddad小裂纹理论,结合Chaboche损伤累积模型和Walker裂纹扩展模型,考虑压气机叶片载荷谱包含多应力比、过载、变幅加载等特性,建立一个既可预测裂纹萌生寿命、又可预测裂纹扩展寿命的综合寿命模型。叶片振动特性分析可以为损伤识别提供帮助,而损伤程度是裂纹扩展寿命预测的主要依据。建立裂纹叶片几何模型和有限元模型,分析裂纹参数(裂纹长度、裂纹位置)变化对叶片振动特性的影响规律,探讨裂纹参数变化引起的叶片频率转向和振型转换等耦合振动问题;基于裂纹叶片振动特性分析结果和RBF神经网络理论,对叶片裂纹参数识别进行研究。根据发动机实际运行中的典型工况,将航空发动机运行状态简化为5种典型工作循环,并编制转速谱。综合考虑低周离心载荷、稳态气动载荷和高周振动载荷的高低周复合加载,进行高压压气机叶片应力分析,计算叶片危险节点应力历程,分别对无损叶片及缺口叶片进行全寿命和裂纹扩展寿命预测。
[Abstract]:High pressure compressor blade is a key rotating part of turbofan engine. Its reliability directly affects engine performance and flight safety. During engine service, fatigue fracture is the main failure form of high pressure compressor blade, and crack initiation and propagation gradually under the action of alternating load. If the blade breaks in the process of work, besides affecting the performance of the engine, the high-speed breakaway debris will cause serious secondary damage to the whole rotor system and the casing. It is very important to study the fatigue crack initiation and propagation of high pressure compressor blade for improving the reliability of aeroengine. Blade life assessment runs through the entire life cycle of engine design, manufacture, use and maintenance, therefore, considering the complex and variable operating conditions of an aeroengine, It is of great scientific significance and engineering application to establish an accurate prediction model for fatigue life of high pressure compressor blade. Titanium alloy 6Al 4V has become the main manufacturing material for high pressure compressor blade due to its excellent mechanical properties at medium and high temperature. In this paper, the crack initiation and propagation life of high pressure compressor blade is predicted by the combination of material fatigue test and simulation. The main contents are as follows: the vibration fatigue test of Ti 6Al 4V titanium alloy blade is carried out. Including constant amplitude loading, variable amplitude loading and crack growth test, the influence of stress difference of variable amplitude load and cyclic ratio on the fatigue life of blade under variable amplitude loading is analyzed. The crack initiation and propagation of the blade are studied. The microscopic characteristics of fatigue fracture are observed by using the hyperfield depth microscope and scanning electron microscope, and the stress ratio and overload are further discussed. The influence of the variable amplitude loading factors on the crack growth rate of the blade under high and low cycle composite loading. Based on Haddad's small crack theory, combined with Chaboche damage accumulation model and Walker crack propagation model, considering the characteristics of compressor blade load spectrum including multi-stress ratio, overload and variable amplitude loading, a new method for predicting crack initiation life is established. The comprehensive life model of crack propagation life can also be predicted. The analysis of blade vibration characteristics can provide help for damage identification, and the damage degree is the main basis for prediction of crack growth life. The geometric model and finite element model of crack blade are established to analyze the influence of crack parameters (crack length, crack position) on blade vibration characteristics. The coupled vibration problems of blade such as frequency steering and mode conversion caused by crack parameter change are discussed, and the identification of blade crack parameters is studied based on the analysis results of crack blade vibration characteristics and RBF neural network theory. According to the typical operating conditions in the actual operation of the engine, the running state of the aeroengine is simplified into five typical working cycles, and the rotational speed spectrum is compiled. Considering the low cycle centrifugal load, steady aerodynamics load and high cycle vibration load, the stress analysis of high pressure compressor blade is carried out, and the stress history of blade dangerous node is calculated. The whole life and crack propagation life of lossless blade and notched blade were predicted respectively.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：V235.13

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