TC4-DT钛合金电子束焊接接头裂纹萌生数值模拟及试验研究
本文选题：钛合金电子束焊接接头 + 裂纹萌生模拟 ； 参考：《南京航空航天大学》2017年硕士论文
【摘要】：结构疲劳研究中,广泛采用唯象模型。由于唯象模型无法揭示疲劳破坏的物理机制和过程,使得对疲劳的研究难以深入。近年来,从细观角度来研究材料的疲劳失效成为研究的新热点。本文以TC4-DT钛合金电子束焊接头为研究对象,针对接头不同区域的裂纹萌生展开数值模拟和试验研究,主要研究内容如下:论文采用元胞自动机法模拟获得了焊接接头焊缝区柱状晶组织;采用泰森多边形法模拟获得了母材区及靠近母材处热影响区的等轴晶组织,经与对应区域的实际组织进行对比,证明模拟结果可以很好地描述所研究区域的组织特点。论文基于组织模拟结果,利用自主开发的前处理程序,将所获得的微观组织转入Abaqus平台中;为研究不同晶粒取向对细观破坏的影响,在前处理中赋予晶粒不同的局部坐标系和滑移带,据此建立了TC4-DT钛合金电子束焊接头不同区域不同组织的有限元模型;通过Python语言对Abaqus进行二次开发,将Tanaka位错模型和有限元法结合,完成了对TC4-DT钛合金电子束焊接头不同区域裂纹萌生的过程的模拟,并完成了不同区域疲劳裂纹萌生寿命的模拟。模拟从多维度出发,分别考虑了不同区域、不同载荷水平作用以及晶粒取向不同时的裂纹萌生情况,并对比探索了对裂纹萌生的影响因素,建立了可用于材料细观组织裂纹萌生及循环寿命预测的分析方法和数值模拟模块。论文对TC4-DT钛合金电子束焊接接头进行原位疲劳试验,实时观察了微观尺度上裂纹的萌生和扩展过程,研究了裂纹萌生的机制并探索了裂纹萌生与TC4-DT钛合金电子束焊接头微观组织的关系。论文将数值模拟结果与本试验及文献中的相关疲劳试验的寿命数据进行了对比,初步验证了数值模拟方法的合理性。论文初步探索出了一种基于材料细观组织模拟裂纹萌生的计算模型,能够有效地模拟合金材料及焊接接头焊缝区域的裂纹萌生及寿命。相对传统的唯象模型,效率更高且经济性更好。此外,原位疲劳试验得出了TC4-DT焊接接头短裂纹萌生的过程,从本质上揭示了该材料疲劳的微观机理。
[Abstract]:Phenomenological model is widely used in structural fatigue research. Because phenomenological model can not reveal the physical mechanism and process of fatigue failure, it is difficult to study fatigue deeply. In recent years, it has become a new research hotspot to study the fatigue failure of materials from the viewpoint of meso-scale. Taking TC4-DT titanium alloy electron beam welding joint as the research object, the numerical simulation and experimental study on crack initiation in different regions of the joint are carried out in this paper. The main research contents are as follows: in this paper, the columnar crystal structure in the weld zone of welded joint is simulated by cellular automata method, and the equiaxed crystal structure in the base metal region and the heat-affected zone near the base metal is obtained by Tyson polygon method. By comparing with the actual organization of the corresponding region, it is proved that the simulation results can well describe the organizational characteristics of the studied region. Based on the results of microstructure simulation, the microstructures obtained are transferred to Abaqus platform by self-developed pre-processing program. According to the local coordinate system and slip band of different grains in pretreatment, the finite element model of different structures in different regions of electron beam welding joint of TC4-DT titanium alloy is established, and the secondary development of Abaqus is carried out by Python language. By combining Tanaka dislocation model with finite element method, the process of crack initiation in different regions of electron beam welding joint of TC4-DT titanium alloy has been simulated, and the fatigue crack initiation life in different regions has been simulated. The simulation considers the crack initiation of different regions, different load levels and different grain orientation from multi-dimension, and compares and explores the influence factors on crack initiation. An analytical method and a numerical simulation module are established for predicting the crack initiation and cyclic life of microstructures of materials. In this paper, the in-situ fatigue test of TC4-DT titanium alloy electron beam welded joint was carried out, and the crack initiation and propagation process on the micro scale was observed in real time. The mechanism of crack initiation and the relationship between crack initiation and microstructure of electron beam welding joint of TC4-DT titanium alloy were studied. In this paper, the numerical simulation results are compared with the fatigue life data in this experiment and in the literature, and the rationality of the numerical simulation method is preliminarily verified. In this paper, a computational model for simulating crack initiation based on the microstructure of materials is proposed, which can effectively simulate the crack initiation and life in the weld zone of alloy materials and welded joints. Compared with the traditional phenomenological model, the efficiency is higher and the economy is better. In addition, the process of short crack initiation in TC4-DT welded joint was obtained by in-situ fatigue test, and the microscopic mechanism of fatigue of the material was revealed in essence.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407
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