超声Lamb波在焊缝中传播的数值仿真及实验研究

发布时间：2018-03-31 05:11

本文选题：Lamb波　切入点：频散特性　出处：《哈尔滨工业大学》2017年硕士论文

【摘要】：大型环缝焊接构件在石油、化工及核电等现代工程领域应用广泛。为了保证焊缝构件的生产质量及使用安全性,实施可靠的无损检测是生产加工及使用过程中必要的技术环节。动态扫查方式的常规超声检测在工程应用中存在着耦合困难、相关处理工艺复杂、检测效率低下等弊端。针对这一问题,本文研究利用超声Lamb波可长距离传播的特点对大型焊缝实现全缝静态、快速检测。本文首先从Lamb波基本理论入手,推导出特征频率方程,并用Matlab编程求解所得方程,绘制了铝板的频散曲线。根据频散曲线及斜楔声速计算现有频厚积下各模态斜入射的激励角度,得到不同模态激励角度及其对应的群速度和相速度,为后续的数值仿真及实验研究提供理论依据。数值仿真对辅助认知检测机理及指导实际检测有重要意义。首先研究确定了有限元模拟的各个参数、条件及Lamb波声场的激发方式。在此基础上模拟了Lamb波在焊缝及薄板结构中的传播及声场分布,并进行相关实验,验证了仿真结果的可靠性。分析了焊缝中Lamb波的泄漏和衰减,对比结果表明:焊缝这样的几何结构可作为Lamb波的“波导”,即在有焊缝的情况下,相当部分的能量被集中于焊缝中,这对焊缝缺陷检测是十分有利的。进一步仿真研究了Lamb波的波场分布及其与缺陷体的作用,分析了Lamb波检测时缺陷定位及尺寸识别效果,结果表明:A0导波能较为准确地识别缺陷位置,而A1模态对缺陷的位置信息不如A0模态敏感;无论是表面缺陷还是埋藏缺陷,A1模态无法表征缺陷的尺寸信息;A0模态与缺陷尺寸有良好的线性关系,并且发现A0模态更适合判别埋藏缺陷。搭建Lamb波静态检测实验系统,进行传播特性及缺陷检测的实验研究。Lamb波传播及声场特性的仿真结果和实验结果对应较好;对含人工槽缺陷的试件进行检测研究,检测结果表明,A0波对于缺陷定位检测精度较高,且回波能量与缺陷尺寸线性相关,可用来表征缺陷尺寸信息,与仿真计算得到的规律一致,这表明Lamb波可用来进行缺陷的定位检测及尺寸评估;对孔洞类缺陷进行检测研究,实验结果表明,本研究静态检测方法的检测灵敏度达到:当检测距离大于200mm时,能识别到1mm直径的孔缺陷。
[Abstract]:Large girth welding components are widely used in modern engineering fields such as petroleum, chemical industry and nuclear power. The implementation of reliable nondestructive testing (NDT) is a necessary technical link in the process of production, processing and use. The conventional ultrasonic testing of dynamic scanning is difficult to be coupled in engineering application, and the related processing technology is complex. The detection efficiency is low. Aiming at this problem, this paper makes use of the characteristics of long distance propagation of ultrasonic Lamb wave to realize static and fast detection of large weld seam. In this paper, the characteristic frequency equation is derived from the basic theory of Lamb wave. The dispersion curve of aluminum plate is plotted by Matlab programming. According to the dispersion curve and the sound velocity of wedge, the excitation angles of different modes and their group velocities and phase velocities under the existing frequency thick product are calculated. It provides theoretical basis for subsequent numerical simulation and experimental research. Numerical simulation is of great significance to assist cognitive detection mechanism and guide practical detection. Firstly, the parameters of finite element simulation are studied and determined. On the basis of this, the propagation and sound field distribution of Lamb wave in weld and thin plate structure are simulated, and the reliability of the simulation result is verified by relevant experiments. The leakage and attenuation of Lamb wave in weld seam are analyzed. The results show that the geometrical structure of the weld can be used as the "waveguide" of Lamb wave, that is, in the case of weld, a considerable portion of the energy is concentrated in the weld. This is very beneficial to weld defect detection. Further, the wave field distribution of Lamb wave and its effect on defect body are studied, and the effect of defect location and size identification on Lamb wave detection is analyzed. The results show that: A0 guided wave can accurately identify the defect position, while A1 mode is less sensitive to the defect position information than A0 mode. No matter the surface defect or the buried defect A1 mode can not represent the size information of the defect, the A0 mode has a good linear relationship with the defect size, and it is found that the A0 mode is more suitable to distinguish the buried defect. The Lamb wave static detection experimental system is built. The simulation results of Lamb wave propagation and sound field characteristics correspond well with the experimental results. The results show that the accuracy of A0 wave detection for defect location is high, and the echo energy is linearly related to the defect size, which can be used to characterize the defect size information, which is consistent with the law obtained by simulation. The results show that Lamb wave can be used to detect defects and evaluate their size. The experimental results show that the detection sensitivity of the static detection method is as follows: when the detection distance is larger than 200mm, A hole defect that can identify the diameter of 1mm.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG441.7

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