【作者】 程载斌；

【导师】 马宏伟；

【作者基本信息】 太原理工大学 ， 固体力学， 2004， 硕士

【摘要】 管道的破裂是石油、化工等行业中经常面临的一个重要问题。裂纹既可能发生在管道外壁又可能发生在管道内壁，通常致使管道壁厚减薄。传统无损超声检测技术是单点检测，因而，在检测长距离管道时，该方法遇到很大困难。利用纵向超声导波检测管道裂纹的技术可以解决这一难题，检测范围可达数十米，并且它是线检测，因而比单点检测省时、高效。其基本原理是，在管道一端激励出导波沿管道传播，通过监测回波的变化来确定管道缺陷的位置及尺寸等。但是，由于导波的多模态及频散特性，往往又使结果分析异常复杂，所以，选择和激励单一模态导波检测管道可大大简化问题分析的复杂性。 本文针对利用超声导波技术进行管道裂纹检测的问题进行了数值模拟和实验研究。首先对当前本课题研究领域的进展作了综述，简要介绍了超声导波技术的基础知识。其次，在前人理论工作的基础上，详细推导了空心圆管中的导波理论，得出了空心圆管中柱面导波和周向导波的频散方程，对频散曲线进行了数值计算；分析了空心圆管中导波的模态，并探讨了如何选取适合管道裂纹检测的导波模态进行检测；基于脉冲回波原理，并考虑频散及横向效应等因素的影响，提出了减小频散影响的修正系数，并据此给出了简单、直观的管道裂纹检测公式；用有限元程序ANSYS对空心圆管中的导波模态及管道超声纵太原理工大学硕士研究生学位论文向导波裂纹检测进行了数值模拟，对激励信号进行了分析计算，找出经HAN小汀NG窗调制的10~巧个单音频叠加激励信号，通过对管道一端周向各节点施加轴向瞬时位移载荷模拟入射导波，同端接收反射波，利用提出的管道裂纹检测公式，对不同裂纹尺寸的单裂纹管道模型进行了大量的数值模拟，模拟结果表明:可较为精确地定位单裂纹位置，对裂纹的周向长度、壁厚减薄程度及裂纹反射面积均可近似确定，但纵向导波对裂纹轴向宽度并不敏感，管道末端的边界条件对裂纹识别结果的影响很小，模拟结果与理论及前人实验结果吻合较好;通过数值模拟，首次成功地对双裂纹位置进行了准确定位，并对结果进行了讨论。最后进行了空心圆管单裂纹定位实验，取得了初步成果。更多还原

【Abstract】 Crack in pipe work is one of main problems in the oil, chemical and other industries. These cracks can occur at the outer or inner surface of the pipe and can lead to a serious decrease of pipe wall thickness. Traditional ultrasonic nondestructive testing techniques are single position measurements, therefore, they tend to be too slow to make that long distance inspection is almost impossible. An alternative method to pipe detection is to excite guided waves, which can propagate tens of meters along pipe, and to monitor the response of the pipe by measuring changes in the received signal. An ultrasonic inspection technique using guided waves was applied to detect and determine the exact location of crack in long steel pipes. However, many modes of guided waves are generated due to guided waves’ multi-modes characteristic in the inspection. To select and excite single mode to detect the pipe can obviously simplify the analysis complexity.In this paper, numerical simulation and experimental investigation on crack detection in pipe using ultrasonic guided waves were carried out. Firstly, some main studies and progresses in this field were reviewed, and the relative theoretical basis was introduced. Secondly, based on the former theoretical introduction,the theories of guided wave in hollow circular cylinder were deduced in details. The characteristic equations of cylindrical and circumferential guided wave were obtained and the corresponding dispersion curves were numerically calculated. At the same time, guided wave modes in hollow circular cylinder were analyzed to choose the appropriate mode for guided wave detection in pipe. The simple and intuitionistic formulas were given based on pulsed echo principle, in which the effect of dispersion and transverse sensitivity were considered. By using finite element code ANSYS, a finite element model with circumferentially oriented through-thickness crack of various circumferential length, depth and axial width was built to simulate crack detection in pipe using longitudinal guided wave. 10 to 15 cycles narrow band signal modulated by HANNING window was chosen for excitation which is simulated by prescribing axial transient displacement at one end of pipe model. The echo can be received at the same end. The results of numerical simulation showed that the single crack position could be accurately identified. The circumferential length, depth and cross section area of crack could be approximately determined by reflection coefficient, which was defined as the amplitude of the reflected signal divided by the amplitude of the incident signal, as a function of them. It can also be found that the longitudinal guided wave detection is not sensitive to axial width of crack and the results are merely affected by boundary condition. The results of theoretical and numerical simulation are greatly agreed with the former investigation. Furthermore, double cracks positions were accurately identified for the first time and the results were discussed. Finally, the experimental investigation on crack detection in hollow circular cylinder is performed and the preliminary results are obtained.更多还原