【作者】 郑建才；

【导师】 吴昭同；

【作者基本信息】 浙江大学 ， 机械制造及其自动化， 2003， 硕士

【摘要】 涡流无损检测技术具有灵敏度高、检测速度快、非接触等特点广泛应用于厚度检测和缺陷探伤，它的原理是当载有交变电流的检测线圈靠近金属导体时在导体中产生涡流，该涡流又影响原磁场，使得线圈的阻抗和感应电压发生变化，通过分析阻抗或感应电压的变化来获得被测导体的信息。 本文结合我国某飞机工业集团公司的《飞机蒙皮贴胎间隙检查仪方案设计》研究项目，研究了涡流技术在多层金属板厚度或板间间隙检测的可行性，并进行实验验证。论文的主要内容和研究成果如下： 1)本文参照Luquire、uzal和雷银照等人的多层厚度涡流检测的数学模型，推导了一个半无限大空间内的三层厚度电涡流检测数学模型。利用Maxwell电磁方程组，通过求解矢量磁位的边值问题得到了矢量磁位的解析解，进而导出了媒质上方放置式空心线圈的阻抗增量解析式，并对阻抗变化表达式进行单层板厚度和三层板间隙的检测模型进行了仿真。仿真结果表明：对于单层板的厚度检测，探头阻抗的变化值随着板厚的增加而逐渐减小，而对于中间层间隙检测，则是探头阻抗变化值随着间隙值的增加而逐渐增加；当上层板的厚度增加，则在相同间隙条件下的阻抗变化幅值减小。 2)论述了多层厚度电涡流检测实验系统研制过程，详细叙述了检测实验系统的硬件功能框图，并对相应的硬件电路进行了设计。针对原电路难以调零的缺点，提出了新的电子平衡电路方案，设计了新的电子平衡电路，新的平衡电路调零精度高，速度快，平衡状态可以长时间保持，缺点是难以利用现有电路，成本较高。 3)分析了涡流检测系统的干扰，提出了相应的抗干扰措施，在此基础上对检测探头进行外形设计，提高曲面检测的精度，便于实际应用。 4)研究了智能涡流检测系统的结构，对涡流检测系统的软件部分进行详细的论述，给出了程序框图。采用了一种利用傅立叶描述子来提取涡流检测信号的特征量的方法，输入到人工神经网络进行定量识别的方法，得出缺陷的尺寸。并将神经网络方法和最小二乘法多项式拟合法进行了比较。 5)对检测数据进行了最小二乘法的多项式拟合，结果表明：对于间隙检测随着铝板间间隙的增大，感应电压幅值增大；上层板厚度的增加，电压幅值则减小。而对于单板厚度检测，则是随着板厚的增加，感应电压幅值减小。实验验证了多层厚度检测数学模型的正确性。另外还将系统应用于经过处理的非金属贴胎的间隙检测，实验结果表现比较强的规律性，在一定的间隙范围内，随着蒙皮与胎模之间间隙的增大呈上升趋势。更多还原

【Abstract】 Eddy Current Nondestructive Testing (ECNDT) is widely used to detect the thinness and defects of the sample, because of its characteristics of non-contact, high sensitivity and ease of detection. The principle of ECNDT is that: when a probe coil with the AC exciting source is put near a sample, eddy current will be produced in the sample which will conversely affect the impedance of the coil according to the Farad Theorem. Any un-uniformity in the sample will change the impedance of the coil and the output voltage. Monitoring the change will give us useful information about the sample.The paper begins from analyzing the principle of ECNDT, studies the feasibility of the clearance detection between two metal plates using eddy current, furthermore makes experiment research. The content of the dissertation is as follow:(1) An eddy current testing model of multi-layered metal structure was presented in the light of the work of Luquire and others. Using Maxwell electromagnetic equations, by solving the boundary-value problem of magnetic vector potential, analytical expression to impedance increment of the solenoid coil in eddy current testing of the medium in half space was given. Theoretical result was modeled in computer. Results showed the validity and feasibility of the model.(2) In the paper the structure of intelligent eddy current testing system was studied. The function frame of the system and its hardware circuit were introduced. To the defect of the system hard to equilibrate , a new circuit frame to make equilibrium was presented(3) Based on the analysis of interferences of the circuit, some relative means were taken to restrain the interferences. Furthermore in order to detect surface conveniently and to improve the testing accuracy some designs of the probe were introducer.(4) An approach involving the use of Fourier descriptors for the extraction of eddy current signal characteristics before their inputting into neural network for quantitative analysis was presented. The results showed that the output of neural network had high analysis accuracy.(5) Lastly the testing data was taken to curve fitting in least squares. The fitting results showed that: to the clearance detection the amplitude of output voltage would increase when the clearance between two metal plates increased. Otherwise ,the amplitude would decrease; to the thinness testing the amplitude would decrease when the thinness became thick. The experiment proved the correctness and feasibility of the eddy current testing model.更多还原