蠕变疲劳交互作用下多晶金属材料的损伤研究和寿命预测

发布时间：2018-01-21 21:46

本文关键词： 蠕变疲劳孔洞演化损伤模拟寿命预测　出处：《清华大学》2016年博士论文　论文类型：学位论文

【摘要】：现代工业正在向着高温、高压的方向快速发展,在石油化工、航空航天、能源动力等行业中,越来越多的机械设备和构件,如大型燃气轮机、航空发动机、核电站设备、冶金机械等长期在高温高压条件下工作,承受着越来越高的温度和载荷作用,在这样的条件下,严重威胁其安全的蠕变和疲劳破坏问题日益突出,特别是蠕变和疲劳两者交互作用下的破坏事故不断发生,早已引起人们的重视。单纯的蠕变或疲劳问题是比较传统的工程问题,而蠕变疲劳交互作用下的损伤问题更值得我们关注,也更符合上述实际工程中的情况。本文从微观模型、模拟演化和寿命预测等几个方面对几种典型的多晶金属材料在蠕变疲劳交互作用条件下的损伤问题进行了分析。从微观角度出发,改进并应用孔洞增长演化方程,利用Voronoi多边形剖分方法,建立多晶金属材料的晶粒晶界分布模型,并随机生成了晶界中的孔洞萌生点,计算了晶界中孔洞在蠕变疲劳交互作用条件下的演化规律。同时定义了孔洞占晶界的百分比为参数的损伤变量,研究了其随载荷、温度、保载时间、晶粒尺寸等影响因素的变化规律。为了更准确和直观地描述孔洞演化过程,通过编制程序,建立了能够表现微观孔洞演化的有限元中循环计算方法和流程,其中考虑到了每个载荷循环中应力和孔洞都会互相影响和随时间变化,更符合真实工况。这种计算方法和流程可以应用于多种典型多晶金属材料的孔洞演化分析上。在基于Gurson本构的研究疲劳问题的损伤模型中,孔洞百分比是一个重要的参量,在此损伤模型中引入由蠕变效应导致的孔洞百分比的增加项,并将其用于蠕变疲劳交互作用条件下的情况。通过一个滚动轴承模型的验证,证明改进模型较纯疲劳条件下的损伤有显著增加,也实现了一种通过孔洞百分比分析蠕变疲劳共同损伤的标量方法。最后,对四种常用的疲劳蠕变交互作用下寿命预测方法进行了评估和比较,并选取其中精度较高且更有较明确物理含义的滞回能量法的一个改进模型对Grade91钢进行了更好的蠕变疲劳寿命预测。
[Abstract]:Modern industry is developing rapidly in the direction of high temperature and high pressure. In petrochemical, aerospace, energy power and other industries, more and more mechanical equipment and components, such as large gas turbines, aero-engines. Nuclear power plant equipment, metallurgical machinery and other long-term working under the conditions of high temperature and high pressure, bear more and more high temperature and load, in such conditions, serious threats to its safety of creep and fatigue damage problems become increasingly prominent. Especially, the failure accidents under the interaction of creep and fatigue have been paid more and more attention. Simple creep or fatigue is a traditional engineering problem. The damage problem under the interaction of creep fatigue is more worthy of our attention, but also more in line with the actual engineering situation mentioned above. The damage problems of several typical polycrystalline metal materials under the interaction of creep fatigue are analyzed in the aspects of simulation evolution and life prediction. The grain boundary distribution model of polycrystalline metal materials is established by using the Voronoi polygon method and the evolution equation of pore growth is improved. The pore initiation points in the grain boundary are generated randomly. The evolution law of voids in grain boundaries under the condition of creep fatigue interaction is calculated. At the same time, the percentage of voids in grain boundaries is defined as the damage variable of parameters, and the effect of load, temperature and loading time is studied. In order to describe the evolution process of the pore more accurately and intuitively, the cyclic calculation method and flow chart of finite element which can represent the evolution of the micro pore are established by compiling the program. It is considered that the stress and the hole will affect each other and change with time in each load cycle. This method and process can be applied to the pore evolution analysis of several typical polycrystalline metal materials. In the damage model of fatigue problem based on Gurson constitutive model. The percentage of holes is an important parameter, and the increase of the percentage of holes caused by creep effect is introduced in the damage model. It is used in the case of creep fatigue interaction. Through the verification of a rolling bearing model, it is proved that the damage of the improved model is significantly increased than that of the pure fatigue condition. A scalar method is also implemented to analyze the creep fatigue joint damage through the percentage of voids. Finally, the life prediction methods under the interaction of fatigue and creep are evaluated and compared. An improved model of hysteretic energy method with higher precision and clearer physical meaning is selected to predict the creep fatigue life of Grade91 steel.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG115

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