基于有限元模拟方法的蠕变疲劳交互作用下裂纹萌生研究

发布时间：2018-06-16 15:23

本文选题：蠕变疲劳交互 + 损伤　；参考：《天津大学》2014年硕士论文

【摘要】：对于电厂高温结构,在服役过程中,结构除了承受高温稳定载荷外,由于重复的启动停止还会产生变化的载荷,启停中变化的载荷以及运行过程中稳定的载荷导致蠕变-疲劳的交互作用。对于初始无缺陷结构,裂纹的萌生寿命在结构失效寿命中占据很大的比例,研究蠕变-疲劳交互作用下裂纹的萌生及影响因素具有重要意义。通过结合初始应力应变场与连续损伤力学理论以及单元失效和裂纹萌生准则,构建了蠕变-疲劳交互作用下裂纹萌生的预测模型,将模型编写为UMAT耦合到ABAQUS有限元分析软件中并进行损伤的计算,实现了初始无缺陷结构蠕变-疲劳交互作用下裂纹萌生的有限元模拟,分析了影响裂纹萌生位置和裂纹萌生寿命的因素。分析表明危险部位的应力水平和塑性应变水平是影响裂纹萌生的关键因素,裂纹萌生于应力集中和塑性应变集中的位置;通过与线性累计损伤理论对比发现,裂纹萌生位置蠕变损伤和疲劳损伤具有相互促进作用,蠕变疲劳的交互作用使裂纹萌生寿命减小;模拟了三种不同的蠕变和疲劳载荷的加载顺序,结果表明加载顺序对裂纹萌生位置损伤的累积具有显著影响,承受蠕变载荷后再施加后续循环载荷时结构总损伤更严重,从而使裂纹萌生寿命更短;应力集中系数与循环寿命的对数近似呈线性关系,且应力集中系数越大,裂纹萌生时蠕变损伤分量越大。
[Abstract]:For high-temperature structures in power plants, in the course of service, in addition to withstanding high-temperature stable loads, because of repeated startup stops, they will also produce variable loads. The variable load during startup and stop and the steady load during operation lead to the creep-fatigue interaction. For the initial faultless structure, the crack initiation life occupies a large proportion of the failure life of the structure. It is of great significance to study the crack initiation and its influencing factors under the creep-fatigue interaction. Based on the theory of initial stress-strain field and continuous damage mechanics and the criterion of element failure and crack initiation, a prediction model of crack initiation under the interaction of creep and fatigue is established. The model is programmed as UMAT coupled to Abaqus finite element analysis software and the damage is calculated. The finite element simulation of crack initiation under the creep-fatigue interaction of the initial defectless structure is realized. The influence factors of crack initiation position and crack initiation life are analyzed. The analysis shows that the stress level and plastic strain level are the key factors affecting the crack initiation, and the crack initiation is in the position of stress concentration and plastic strain concentration, and it is found by comparison with the linear cumulative damage theory that the stress level and the plastic strain level are the key factors affecting the crack initiation. The creep damage at crack initiation position and fatigue damage promote each other, and the interaction of creep fatigue reduces the crack initiation life, and simulates the loading sequence of three different creep and fatigue loads. The results show that the loading sequence has a significant effect on the cumulative damage of crack initiation position, and the total damage of the structure is more serious when the creep load is applied after the subsequent cyclic loading, which makes the crack initiation life shorter. The logarithmic relationship between the stress concentration factor and the cyclic life is linear, and the larger the stress concentration factor is, the larger the creep damage component is during crack initiation.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM621

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