焊接管节点应力分布规律评估新方法研究

发布时间：2018-01-03 06:17

本文关键词：焊接管节点应力分布规律评估新方法研究　出处：《大连理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：圆管焊接节点在海洋工程领域有着极其广泛的应用。由于管节点在焊缝交线处结构形式非常复杂,会产生严重的局部应力集中,加上焊接过程引入的宏观和微观缺陷,使得管节点在风、浪、流等各种随机环境载荷的联合作用下处于非常复杂的交变应力状态,容易出现疲劳破坏；并且,疲劳评估的最危险点可能出现在沿焊缝交线的任意位置。工程上常用的基于表面插值算法的热点应力法无法对焊趾位置复杂的应力状态进行准确的描述：首先,目前的绝大部分工作均集中于热点应力峰值的计算而忽略了其沿管壁厚度方向及焊缝交线的分布规律；其次,研究中多采用壳单元对管节点进行模拟,无法充分考虑焊趾尺寸对焊缝位置应力分布产生的影响。因而,对于受到多轴疲劳载荷作用的复杂焊接管节点,传统的疲劳评估应力计算方法仍存在一些问题。为保证海洋平台整个服役过程中的安全,研究焊接管节点在复杂载荷作用下的应力分布规律,建立能够应用于实际工程结构的多轴疲劳强度评估方法,在海洋工程领域具有非常重要的意义。本文以T型管节点为例,将一种新的零点结构应力法用于其疲劳评估应力的计算。计算过程中,为更加准确的考虑焊缝尺寸对管节点应力分布产生的影响,文中采用三维的20节点块体单元对管节点的支管、主管以及焊缝进行了详细建模；新方法充分考虑裂纹的扩展方向,以管壁厚度方向上非线性峰值应力为零的一点作为疲劳评估点,以该点处的结构应力作为疲劳评估应力。该结构应力可直接通过有限元计算结果后处理得到,方便用于管节点的多轴疲劳寿命预测；另外,由于评估位置取在管壁外表面下方一点,可在一定程度上考虑应力梯度对疲劳寿命的影响。在此基础上,通过与公开发表的疲劳试验数据进行比较,验证了本文方法应用于管节点疲劳强度评估的适用性和正确性。最后,本文基于大量的有限元数值计算,提出了T型管节点在各基本载荷作用下的应力集中系数参数方程,并对参数方程的精度进行了验证。
[Abstract]:Circular pipe welded joints are widely used in the field of offshore engineering. Due to the very complex structure form of pipe joints at the weld intersections, serious local stress concentration will occur. Combined with the macroscopic and microcosmic defects introduced in the welding process, the pipe joints are subjected to very complex alternating stress states under the combined action of wind, wave, flow and other random environmental loads, which are prone to fatigue failure. And... The most dangerous point of fatigue assessment may appear anywhere along the intersection line of weld seam. The hot spot stress method based on surface interpolation algorithm can not accurately describe the complex stress state of weld toe position in engineering: firstly. At present, most of the work focuses on the calculation of the peak stress of hot spot and neglects the distribution law along the direction of pipe wall thickness and the intersecting line of weld. Secondly, the shell element is often used to simulate the pipe joints, which can not fully consider the influence of weld toe size on the weld stress distribution. Therefore, for the complex welded pipe joints subjected to multiaxial fatigue load. There are still some problems in the traditional fatigue assessment stress calculation method. In order to ensure the safety of offshore platform during the whole service process, the stress distribution law of welded pipe joints under complex loads is studied. It is of great significance to establish a multiaxial fatigue strength evaluation method which can be applied to practical engineering structures. In this paper, T-tube joints are taken as an example. A new 00:00 structural stress method is used to calculate the fatigue assessment stress. In the calculation process, the effect of weld size on the stress distribution of pipe joints is considered more accurately. In this paper, the three-dimensional 20-node block element is used to model the branch pipe, the supervisor and the weld seam of the pipe joint in detail. The new method takes the crack propagation direction into account and takes the point where the nonlinear peak stress is zero in the direction of pipe wall thickness as the fatigue assessment point. The structural stress at this point is taken as the fatigue assessment stress, which can be obtained directly by the post-processing of the finite element calculation results, which is convenient for predicting the multiaxial fatigue life of pipe joints. In addition, the influence of stress gradient on fatigue life can be considered to some extent because the evaluation position is below the outer surface of pipe wall. On this basis, the fatigue test data are compared with published data. The applicability and correctness of the proposed method applied to the fatigue strength assessment of pipe joints are verified. Finally, a large number of finite element numerical calculations are carried out in this paper. The parameter equation of stress concentration factor for T-tube joints under various basic loads is proposed and the accuracy of the equation is verified.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG404

【共引文献】