内压作用下斜接接管结构裂纹萌生预测研究

发布时间：2018-04-26 20:09

本文选题：裂纹萌生 + 结构参数研究　；参考：《兰州理工大学》2015年硕士论文

【摘要】：随着我国对境外能源依赖度的不断增加,在陆地建设一万公里量级以上的油气管道及相应的集输压力容器己变得十分普遍。斜接接管结构作为油气管网及其附属集输压力容器设计中不可避免的结构形式,虽在整体管网中所占比例不大,但属于整体管网中最为薄弱的环节之一,常常产生各种形式的失效和破坏。它的安全稳定运行不仅涉及到国家能源战略的安全,更牵扯到管道所经地域和国家环境保护的重要责任。本文针对内压作用下理想的(没有初始缺陷的、没有焊接带来的不利影响的)斜接接管结构进行裂纹萌生预测研究,并总结分析斜接接管结构的结构参数、应力应变分布、裂纹萌生预测结果之间的关系,以便在斜接接管设计的初期提供一些结构优化的建议,进而增加其在实际工作中的疲劳寿命。本文采用有限元数值模拟作为主要的数据获取手段并结合理论计算对斜接接管结构的裂纹萌生进行预测,主要包括以下研究内容：1.分析了目前普遍使用的缺口构件裂纹萌生预测方法,对比了它们在斜接接管结构裂纹萌生预测上的步骤和优缺点,并对现有条件进行了评估,选择了一种可行的研究方法。2.针对所选的斜接接管结构裂纹萌生预测方法的需要,通过有限元模拟的手段,考察了斜接接管结构弹性应力集中系数(理论应力集中系数)与无量纲结构参数之间的关系。结果表明,小倾斜角、大开孔率、大的筒体与接管的厚度比、大的筒体径厚比将加剧斜接接管结构的应力集中状况,对其造成不利影响。其中当倾斜角小于45度时弹性应力集中系数大幅增加,在结构设计时应尽量避免。3.考察了斜接接管结构弹性应力最大点(危险点)可能出现的部位,并根据斜接接管结构在应力应变分布上的特点将考察范围锁定在理想的焊缝区可能出现危险点的内相贯线、接管焊趾线、筒体焊趾线这三条危险线上。结果表明,在理想的斜接接管结构中,裂纹萌生始终发生在内相贯线的锐角侧。4.使用局部缺口应力应变方法对斜接接管结构的裂纹萌生进行了预测,得到结构参数对其的影响规律。结果表明,小倾斜角、大开孔率、大的筒体与接管的厚度比、大的筒体径厚比将减小裂纹萌生预测结果,对其造成不利影响。其中当倾斜角小于45度时裂纹萌生预测结果将大幅减少,在结构设计时应尽量避免。5.从概率分析角度对斜接接管结构的裂纹萌生预测进行了可靠性分析。并在给定循环载荷范围下,对60度斜接结构进行了具有一定可靠度的裂纹萌生预测。
[Abstract]:With the increasing dependence on overseas energy in China, the construction of oil and gas pipelines and corresponding gathering and transporting pressure vessels over 10,000 kilometers on land has become very common. As an inevitable structural form in the design of oil and gas pipeline network and its affiliated gathering and transporting pressure vessel, the oblique connection structure is one of the weakest links in the whole pipe network, although it occupies a small proportion in the whole pipe network. Often, various forms of failure and destruction occur. Its safe and stable operation involves not only the safety of national energy strategy, but also the important responsibility of the region of pipeline and national environmental protection. In this paper, the crack initiation prediction of the ideal oblique nozzle structure under internal pressure (without initial defects, without the adverse effect of welding) is studied, and the structural parameters, stress and strain distribution of the oblique connection structure are summarized and analyzed. The relationship between the prediction results of crack initiation in order to provide some suggestions for structural optimization in the initial stage of the design of oblique joints and to increase their fatigue life in practical work. In this paper, the finite element numerical simulation is used as the main data acquisition method and the theoretical calculation is used to predict the crack initiation of the oblique nozzle structure, including the following research contents: 1: 1. This paper analyzes the widely used crack initiation prediction methods for notched members, compares their steps, advantages and disadvantages in the prediction of crack initiation of oblique nozzle structures, evaluates the existing conditions, and selects a feasible research method .2. According to the need of the selected prediction method for crack initiation of oblique nozzle structure, the relationship between elastic stress concentration factor (theoretical stress concentration factor) and dimensionless structural parameters of oblique nozzle structure is investigated by means of finite element simulation. The results show that small inclined angle, large opening ratio, large thickness ratio of cylinder to nozzle, and large ratio of diameter to thickness of cylinder will aggravate the stress concentration of the oblique connection structure, which will have a negative effect on it. The elastic stress concentration factor increases greatly when the inclination angle is less than 45 degrees and should be avoided when the structure is designed. The possible position of the maximum elastic stress point (danger point) of the oblique nozzle structure is investigated, and according to the characteristics of the stress and strain distribution of the oblique connection structure, the investigation range is locked in the intersecting line of the danger point which may appear in the ideal weld zone. The pipe welding toe wire, the cylinder body welding toe wire these three dangerous lines. The results show that in an ideal oblique connection structure, the crack initiation always occurs at the acute side of the intersecting line. Local notch stress strain method is used to predict the crack initiation of oblique connection structure, and the influence of structural parameters on the crack initiation is obtained. The results show that the prediction results of crack initiation will be reduced by small inclination angle, large opening ratio, large thickness ratio of tube to nozzle, and large ratio of diameter to thickness, which will have a negative effect on the prediction of crack initiation. The prediction results of crack initiation will be greatly reduced when the inclination angle is less than 45 degrees, and should be avoided as far as possible in structural design. From the point of view of probability analysis, the reliability analysis of crack initiation prediction of oblique connection structure is carried out. At the given cyclic load range, the crack initiation of 60 degree oblique structure is predicted with certain reliability.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE973

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