高速钢轨快速脉冲涡流检测理论模型与方法研究

The rail-head damages such as stripping or crack will reduce the performance and usability of rail-track. It is one of the significant factors threat the safety operation of high speed railway. Thus the online nondestructive testing (NDT) method is needed for in-service rail-track inspection in high speed. The pulsed eddy current testing (PECT) is a non-contact way to find rail-head cracks via scanning detection in high speed, which can make up the limitations of conventional ultrasonic testing on surface and subsurface cracks inspection. However, the fast PECT is not widely used in the rapid detection of rails, which mainly because the detection mechanism of fast PECT is complicated, and the lift-off effect and velocity effect caused by the unevenness of the track surface during the detection have a great influence on the signal, which increases the difficulty for sensor design and signal processing analysis..The aim of this project is to study the theory and method for fast PECT of rail-head. Firstly, the analytical model of fast pulse eddy current detection for high-speed rail is established. The transfer matrix method, the TREE (Truncated region eigenfunction expansion) method and the control equation construction method for the defect layer are studied. Based on the analytical model, the distribution characteristics of induced eddy current and dynamic eddy current are analyzed, and the lift-off effect and the velocity effect are studied. Secondly, based on the analytical model, the sensing method based on the interaction of the coil coefficient, the lift-off effect and the velocity effect is studied, and the sensor which can be used for the detection environment with the lift-off fluctuation and the speed fluctuation is designed. Thirdly, signals with different lift-off and defect parameters are analyzed, and a defect recognition method based on time-segmented metric of normalized signal are proposed. The defect recognition method is independent of lift-off and speed. Finally, based on the research made above, the sensor is made and the signal processing software is programmed to apply the fast pulse eddy current method to high-speed rail detection.

根据高速钢轨表面及上表面缺陷快速检测的重大需求，针对快速脉冲涡流检测方法在检测机理、提离效应和速度效应研究不充分的问题，从检测模型、传感方法和信号处理方法三个方面对高速钢轨快速脉冲涡流检测展开研究。首先，建立高速钢轨快速脉冲涡流检测解析模型，研究适用于模型求解的传递矩阵法、TREE法及缺陷所在层的控制方程构造方法，并基于此分析感应涡流和动生涡流的分布特点及速度效应与提离效应对信号的影响；其次，以解析模型为基础，研究基于线圈系数、提离效应和速度效应相互作用的传感方法，设计适应提离波动和速度波动检测环境的传感器；然后，分析提离和不同缺陷参数对检测信号的影响，提出与提离无关的基于归一化信号时间分段度量的缺陷识别方法，研究速度对不同缺陷参数特征时间片段的影响，获取速度效应的补偿方法；最后，在上述研究的基础上绕制传感器并编写信号处理软件，获取适用于高速钢轨快速检测的脉冲涡流方法，为现场应用提供指导。

针对钢轨表面及上表面缺陷，本项目应用涡流检测技术对其进行检测，并对其机理、探头设计和特征量进行了分析，取得的主要成果如下：1. 建立了基于TR结构的高速钢轨快速涡流检测解析模型和基于谐振方式的涡流检测解析模型，获取了信号特征及探头结构与参数对其检测性能的影响，指导了后续的探头设计和信号特征分析。2. 设计了基于TR结构的脉冲涡流检测探头，并通过理论分析和实验提出了可用于减小提离效应的特征量-线圈间距交叉点。3. 分析了基于谐振方式的涡流检测系统的信号特征，讨论比较了矩形探头、“8”字形探头和双“D”形探头的性能，结果表明，激励线圈谐振点幅值受提离的影响较小，可在提离波动的情况下用于缺陷评估。4. 针对钢轨不同方向的RCF裂纹，设计了一种柔性差动涡流探头，实验表明该探头可有效抑制提离噪声，且对不同取向的裂纹都有较好的检测能力。同时，适当增大线圈间距可以弥补检测速度和提离高对涡流信号的衰减，从而改善涡流探头的响应。本项目的研究工作丰富了钢轨表面及上表面缺陷的检测方法，有助于推动涡流类检测技术在钢轨检测中的进一步发展和应用。