【作者】 段红燕；

【导师】 李有堂；

【作者基本信息】 兰州理工大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 具有环形缺口的圆轴构件的疲劳问题一直是人们所关注的热点问题。目前单轴缺口疲劳的研究已趋成熟,而多轴缺口疲劳寿命有许多问题尚待解决。在工程实际中,只受单轴应力状态的情况是极少见的。即使外部只受单轴应力状态,在缺口处也往往是处于多轴应力状态,开展缺口轴类零件的疲劳寿命预测研究具有重要的理论意义和工程应用价值。本文通过理论分析和大量实验,系统研究具有环形缺口轴的疲劳寿命问题。论文的主要工作和取得的主要成果如下：(1)总结影响缺口轴疲劳寿命的影响因素并对其分类分析。基于传统的疲劳寿命模型,建立缺口轴的疲劳寿命估算模型,评判几种安全寿命预测模型及其影响因素。基于缺口尖端附近的应力场表达式,得出无量纲因子。应用建立的缺口轴疲劳寿命模型,通过计算,得到了缺口半径、缺口张开角和缺口深度与无量纲因子的关系表达式。结果表明,对具有环形缺口的圆杆,可以把无量纲因子作为表征参量,统一描述环形裂纹、环形钝裂纹和环形切口问题。(2)缺口轴在低周拉压、悬臂弯曲及悬臂弯扭载荷下的疲劳实验研究。设计在立式疲劳试验机上进行弯曲、扭转和弯扭组合疲劳实验的组合夹具；在日本岛津(SHIMADZU EHF-EM100kN)新型电液伺服疲劳试验机上进行具有缺口的圆轴在拉压、悬臂弯曲及悬臂弯扭载荷下的低周疲劳实验。通过实验和分析,获得缺口半径、缺口深度和缺口张开角在三种载荷条件下对缺口轴疲劳寿命的影响。结果表明,缺口半径、缺口深度和缺口张开角都是无量纲因子的函数,而且随着缺口半径逐渐增大,缺口轴的疲劳寿命基本呈现增大的趋势。随着切径比的逐渐增大,缺口轴的疲劳寿命呈下降趋势。缺口张开角在小于90°时,对缺口轴疲劳寿命的影响基本可以忽略,证明了所建立的缺口轴疲劳寿命模型的有效性。(3)针对影响缺口轴疲劳寿命因素多,且各因素间存在交互作用的问题,提出一种基于Matlab的BP人工神经网络的多因素疲劳寿命预测方法。仿真结果表明,这种方法用来预测缺口参数(缺口半径、缺口深度和缺口张开角)对缺口轴疲劳寿命的影响时具有较高的精度、良好的自适应和自学习的智能化特征等优点,克服了传统计算方法计算量大,要依赖于数学模型的缺点。(4)通过悬臂弯扭复合载荷作用下的典型断口分析,获得多轴循环加载下的疲劳裂纹萌生和扩展规律。疲劳裂纹萌生在试样外表面的最大等效应力处,且呈现疲劳裂纹的多源性。疲劳裂纹在试样外表面形成后,呈放射状向内部扩展。随着载荷的加大,瞬断区的撕裂面积逐步增大,且各瞬断区都均偏离中心。分析结果为多轴疲劳过程和疲劳失效机制提供了理论依据。更多还原

【Abstract】 Fatigue of notch component has been the concern matter of people. At present, uniaxial fatigue of the notch component in research has been a lot of ways, but there is no more mature approach about multiaxial loading fatigue life. In engineering practice, there is extremely rare in the uniaxial stress condition. Even if the outside is to be in the uniaxial stress state, multi-axial stress exit in the shaft notch. It is to be important theoretical significance and engineering application value to carry out the fatigue life prediction research. In this paper, through theoretical analysis and a large number of experiments, systematic research has to be carried out the fatigue life of annular gap axis.The main contents of this paper are as follows.(1) The impact factors of the gap-axis fatigue life are be summaried and its to be classified. Based on the traditional fatigue life model, the fatigue life prediction model of gap axis has been established. Several kinds of safety life prediction model and its influencing factors have been evaluated. The expression based on the stress field near the tip gap, dimensionless factor is be obtained. Using the establishment gap axis fatigue life model, through the computation, the relational expression between the gap radius, the gap open angle,the gap depth and the dimensionless factor has been established. The results show that the dimensionless factor can be as the unified parameter to describe the circumferential crack, circumferential blunt crack and ring-shaped crack.(2) In this paper, the fatigue experiments of gap axis have been carried out in the low cycle tension-compression, cantilever bending and cantilever blank tear load. A combined clamp has be designed to carry out the fatigue test in tension-compression, cantilever bending and cantilever blank tear load. The test equipment is a new electro-hydraulic fatigue testing machine made by Japan. The range of models are SHIMADZU EHF-EM100kN. Through experiments and analysis, the relation betwwen gap radius, gap depth, gap opening angle and its fatigue life in the three kinds of load conditions, has been obtained. The result indicated that the gap radius, gap depth and gap opening angle are a function of the dimensionless factor. As the notch radius increases gradually, the gap axis fatigue life show increasing trends.As the cutting diameter ratio increased gradually, fatigue life of the gap axis displayed downward trend. When the gap opening angle is less than 90°, its effect on fatigue life of notch shaft has been ignored. It proved that the model of axial fatigue life was effective and useful.(3) In view of many impact factors on fatigue life, and the interaction of various factors that exist, the author proposes a kind of fatigue life prediction method based on the Matlab BP artificial neural networks. The simulation results show that this method shows the advantage of high precision, good adaptive and self-learning intelligent characteristics to predict the gap shaft fatigue life on gap parameters (gap radius, gap depth and gap opening angle). The calculation method overcomes the traditional shortconging that relys on the mathematical model and a large quantity of calculation.(4) Through the analysis of typical fracture surface in cantilever blank tear load, the law of fatigue crack initiation and expansion has been obtained in multi-axial cyclic loading. Fatigue crack initiates the maximum equivalent stress at the specimen outer surface and presents the multi-origin fatigue crack. Fatigue crack formation of the outer surface of the sample expand to the inner showing radial. Along with load enlargement, tearing area in instantaneous fracture region increase gradually, and instantaneous fracture region is off-center. The analysis result has provided the theory basis for the multi-axial weary process and the fatigue failure mechanism.更多还原