【作者】 邱宝象；

【导师】 高增梁； 王效贵；

【作者基本信息】 浙江工业大学 ， 化工过程机械， 2009， 博士

【摘要】 工程构件的疲劳失效过程通常被分为疲劳启裂和裂纹扩展两个阶段。在现行的疲劳分析框架下,主要采用连续介质力学方法和断裂力学方法,分别分析疲劳启裂寿命和扩展寿命。但从损伤力学角度出发,两个阶段不是两个彼此独立的阶段,而是同属于一个连续的疲劳失效过程。因此,基于疲劳损伤理论,建立统一疲劳启裂和裂纹扩展两个阶段的缺口件全寿命预测方法具有重要的理论价值和现实的工程意义。基于“扩展裂纹”动态裂纹扩展方式和裂纹尖端的疲劳损伤的连续累积过程,确立了疲劳损伤累积过程与裂纹扩展速率之间的数学关系,提出了一个新的、适合描述常幅和变幅加载的“基于连续累积损伤的疲劳启裂和裂纹扩展统一模型”。提出的统一模型构筑了疲劳启裂和裂纹扩展之间的桥梁。克服了现有的模型不能很好地考虑加载历史以及残余应力场和裂纹表面接触之间的交互作用对裂纹扩展影响的缺陷。结合能描述材料非Masing特性的Armstrong-Frederick(A-F)类循环塑性理论和多轴疲劳损伤理论,分别提出了一种基于有限元法的缺口件疲劳寿命预测方法和一种预测非Masing缺口件的疲劳寿命的多轴局部应力应变近似方法。第一种方法考虑了局部塑性变形对缺口根部应力状态的影响。第二种方法适合描述小塑性变形缺口件的多轴应力状态。通过16MnR钢的缺口疲劳试验验证,表明两种方法都能较好地预测拉扭复合加载下的缺口件的疲劳寿命。运用提出的统一模型,预测了缺口件在常幅、高低幅顺序加载和过载下的疲劳启裂寿命、裂纹扩展速率和疲劳全寿命。通过裂纹扩展试验结果验证,表明提出的统一模型不仅能较好地描述缺口件的疲劳启裂和裂纹扩展两个阶段,而且能定量地预测过载或高低幅顺序加载下的裂纹扩展“瞬间加速”和“延时延迟”现象。基于16MnR缺口件的二维有限元数值分析,研究了裂纹扩展过程中裂纹尖端的应力和疲劳累积损伤的演化历史,结果表明:缺口塑性区和裂纹表面接触是缺口短裂纹现象的两个重要影响因素,残余应力场、裂纹表面接触和裂纹本身延伸三者之间的交互机制决定着变幅加载下的疲劳裂纹扩展过程。更多还原

【Abstract】 Fatigue process is often described as the nucleation and growth of cracks to final failure. Under the frame of the fatigue analysis, continuum mechanics methods and fracture mechanics concepts are adopted for the crack initiation life and the propagating life, respectively. However, the nucleation and growth of cracks are not two independent stages, but closely related to the continuous fatigue damage process. Therefore, the establishment of an analysis method on predicting the total life of notched components unifying the fatigue nucleation and growth of cracks has both values of theory and engineering application.On the basis of the propagating crack scheme and the continuous accumulated process of the fatigue damage of the crack tip, the nonlinear mathematical relation between the accumulative history of fatigue damage and the crack growth rate was established. A new model unifying the fatigue nucleation and crack growth based on the continuous accumulated damage was proposed. This model can be applied to the constant and variable amplitude loading. The proposed unified model bridges the gap between fatigue nucleation and growth of cracks during the fatigue damage process. The model can describe well the effects of the loading history and the interaction mechanism between the residual stress and the crack contact on the crack growth behavior.Two fatigue life prediction methods was proposed based on the Armstrong-Frederick type cyclic plasticity theory well describing the non-Masing behavior and the multiaxial fatigue damage theory. One was the fatigue life prediction method based on the finite element method. The other was the multiaxial local stress-strain approximate method predicting the notched component with the non-Masing behavior. The first method considers the effect of the local plastic deformation on the stress state at the notch root. The second method is fit for the notched components with small plastic deformation. The capability of predicting fatigue life for the two methods was checked against the fatigue experimental data of the notched components made of 16MnR steel. It is found that two methods can predict well the fatigue lives of notched components under the axial-torsion loading.The fatigue initiation life, the crack growth rate and the fatigue total life of notched components under the constant amplitude loading, the high-low block loading and the over-loading were predicted based on the proposed model. The unified model was verified by the crack growth experimental results of the notched components made of 16MnR steel. It shows that not only both crack nucleation and crack growth can be modeled simultaneously, but also the initial acceleration and the delayed retardation of crack growth under the overload or the high-low sequence loading can be prediced quantitatively. The histories of the stress and the accumulated fatigue damage of the crack tip were studied based on the 2D finite element method. It shows that the notch influencing zone and the contact of the cracked surfaces are the most important factors resulting in the short crack behavior. The overall crack growth process under the variable amplitude loading is controlled by the interaction mechamsm among the crack surface contact and the residual stress field and the enhanced cyclic plasticity due to the crack advance.更多还原