高速漏磁检测中钢轨磁i化强度的研究

对钢轨裂纹进行高速漏磁巡检时，钢轨的磁化强度直接影响缺陷漏磁场的产生及检测灵敏度。研究了巡检速度、励磁激励和磁轭磁极距被测钢轧的距离（提离）三个因素对钢轨材料磁化强度的影响。通过分析缺陷漏磁检测信号的幅值、检测磁路空气隙处的磁场强度、钢轨材料的磁导率变化得出：巡检速度在2～55m／s范围内时，巡检速度提高，有利于提高高速漏磁裂纹检测的灵敏度；同时，励磁激励电压增加和提离减小都将有利于钢轨材料的磁化强度，从而有利于提高高速漏磁裂纹检测的灵敏度。．     

基于三维霍尔传感器的钢轨缺陷漏磁检测系统

为检测钢轨顶面的剥离、裂纹等缺陷,设计基于三维霍尔传感器的钢轨缺陷漏磁检测系统.采用钕铁硼环形永磁体对钢轨检测区域进行垂直于钢轨方向的励磁,并将检测车的车轮轮轴同时作为励磁回路的磁扼,由ARM单片机采集三维霍尔传感器检测的缺陷漏磁场数据.在钢轨顶面人工制作一系列横向矩形凹坑缺陷样本,检测结果表明:钢轨缺陷三维漏磁检测系...     

基于电磁原理的钢轨裂纹高速在线巡检方法

由于非接触式检测的优势,电磁无损检测技术具有实现铁路钢轨裂纹高速在线巡检的可行性,但检测探头与被测钢轨间的快速相对运动引起的速度效应会对巡检结果带来较大影响。从电磁场基本理论出发,对高速漏磁检测中的速度效应进行了分析;依据速度因素的特点提出了钢轨裂纹高速在线电磁巡检的方法,其特征在于采用直流励磁激励的磁轭分别对钢轨踏面进行纵向和横向磁化,检测探头采用布置在磁轭两磁极中间位置的三维霍尔传感器和三维检测线圈以及缠绕在磁轭臂上的检测线圈。在高速无损检测试验平台上的试验结果表明,提出的巡检方法可以有效实现钢轨裂纹的高速在线巡检,且不同方法对不同类型的钢轨裂纹缺陷识别各有优势,方法互补之后可以实现不同类型钢轨以大于200 km/h速度在线巡检及缺陷的有效识别。     

钢轨表面缺陷漏磁检测的三维磁场分析

漏磁检测技术通常测量垂直和平行于缺陷表面的漏磁场分量,来实现对缺陷的定量分析。然而,对于钢轨表面的复杂裂纹,传统的方法很难准确检测。为了克服这种检测方法存在的不足,采用三维磁场测量方法以及有限元法对缺陷漏磁场的三维分布情况进行了分析。在此基础上设计了一套适合钢轨表面缺陷检测的三维漏磁检测系统,并对人工缺陷样例进行了检测。结果表明,漏磁信号垂直分量包含重要的缺陷信息,特别是对于与钢轨走向不垂直的缺陷。     

钢轨漏磁检测的速度效应

随着铁路列车速度与运量的增加,对钢轨检测速度的要求也不断提高,原有静态条件下的缺陷识别方法需要加以改进。为此研究了钢轨漏磁检测的速度效应。首先通过公式推导,从理论上讨论了检测速度对漏磁信号的影响;然后以有限元方法为基础,在Ansoft软件中建立了研究模型,仿真分析了不同检测速度时的信号差异,总结得出了一些有意义的结论;最后以裂纹的深度和宽度检测为例,研究了检测速度对特征信号的影响规律。     

钢轨疲劳斜裂纹垂向磁化检测仿真

在分析典型滚动接触疲劳裂纹扩展特征,介绍垂向磁化检测原理及巡检方法的基础上,提出了一种采用垂向磁化场对钢轨疲劳斜裂纹进行电磁检测的方法。通过建立有限元模型,仿真分析了表面斜裂纹与钢轨顶面夹角、沿轨面下转向扩展角度、扩展深度及延伸长度、近表面裂纹埋藏深度与垂向磁化检测信号的关系。结果表明,该方法能有效检测材料表面和近表面斜裂纹及其沿轨面下的扩展特征,有助于高速铁路钢轨疲劳伤损的检测和故障早期预警。     

裂纹漏磁场的数值模拟

漏磁检测技术广泛应用于储罐底板扫查、管道内壁缺陷检测中。文章以裂纹漏磁场为研究对象,以麦克斯韦方程组为理论基础,以数值模拟为手段,建立裂纹漏磁场三维静态数值模拟模型,用数值模拟和试验方法研究裂纹深度、宽度、裂纹倾斜角度以及裂纹间距等参数对裂纹漏磁场的影响,得到裂纹参数与裂纹漏磁场幅值之间的关系。结果表明：裂纹倾斜角度对裂纹漏磁场幅值影响显著,因此在工程实际检测中,要从不同方向进行漏磁扫描,以防止漏检;当两条裂纹间距〈5mm时,裂纹漏磁场将产生叠加。数值模拟结果与试验数据较为一致,表明所用数值方法的有效性。文章所得结论对裂纹漏磁检测工程实践有重要的拳者意义。     

钢轨轨底斜裂纹的超声导波散射特性

钢轨轨底斜裂纹的超声导波散射特性是超声导波检测钢轨轨底技术的基础。首先对钢轨轨底导波传播特性及激发频率对导波散射特性的影响进行了数值分析,再进一步基于ABAQUS软件建立了钢轨轨底不同角度斜裂纹散射特性的有限元模型,对横向振动模态和垂直振动模态下钢轨轨底不同角度斜裂纹的散射特性进行了分析。数值分析和波场快照显示,横向振动模态较垂直振动模态下超声导波在钢轨轨底斜裂纹上的频散相对严重,垂直振动模态下导波检测钢轨斜裂纹效果更好,为后续钢轨轨底导波检测试验提供了理论基础。     

三轴漏磁缺陷检测技术

针对轴向裂纹等管道缺陷类型的检测,基于漏磁检测原理,研究了三轴漏磁管道缺陷检测技术.通过对缺陷漏磁矢量场的研究,将漏磁场分为轴向、径向和周向三个分量.利用ANSYS仿真软件,建立励磁系统模型,仿真出三维磁场磁通密度矢量分布图,模拟缺陷漏磁场分布.研制实验平台,采用霍尔传感器制成三轴漏磁检测探头,检测出漏磁场三个方向的漏磁信号.结果表明,三轴漏磁缺陷检测技术可以反映较多缺陷信息,有助于检测特殊类型缺陷.     

基于有限元的管道裂纹漏磁检测仿真分析

提出一种油气管道裂纹漏磁场检测的数学分析方法。先根据麦克斯韦方程组推导出漏磁场数据分析模型。其次,利用三维有限元分析原理在Ansys环境下建立数学仿真模型。再将仿真结果与实际测试数据进行比较,确定该方法的可靠性。最后,通过仿真分析得出了裂纹几何参数(深度和宽度等)对漏磁信号特征的影响规律,并给出它们的关系曲线。该方法为实际利用漏磁场分布检测油气管道裂纹提供了重要的依据。     

基于三维数值模拟的焊缝缺陷漏磁场分析

漏磁检测技术对钢板对接焊缝检测鲜有应用,根据铁磁性焊缝的特点,针对焊接结构中较敏感的裂纹缺陷,探讨应用漏磁法检测钢板对接焊缝裂纹缺陷。采用有限元数值模拟方法(FEM),建立了焊缝三维FEM模型;对比分析焊缝不同区域存在裂纹时漏磁场分布规律;建立不同焊缝余高包含相同尺寸裂纹的三维FEM模型,分析由于焊缝余高的存在对裂纹检出率的影响;研究在焊缝余高3 mm结构条件下,漏磁场磁感应强度分量峰值随裂纹深度的变化规律,得到漏磁场相关对比分析曲线。仿真结果表明:漏磁法适用于钢板对接焊缝缺陷的检测研究;焊缝余高越小,可获得更高的缺陷检出率;漏磁场磁感应强度分量峰值均随裂纹深度的增加呈递增趋势。     

高速铁路钢轨RCF伤损特征及NDT研究进展

随着我国高速列车的大量开行,滚动接触疲劳（RCF）伤损成为了高速铁路钢轨的主要伤损,严重威胁行车安全。本文介绍了我国提速段高速铁路钢轨的滚动接触疲劳伤损的类型、特征和发展模式。相关机构的调研和分析结果表明,轨头裂纹和隐伤是我国提速段钢轨最主要的RCF伤损,且伤损类型与钢轨的强度级别有关。同时介绍了钢轨RCF伤损的无损检测方法研究情况,重点阐述了低频超声表面波检测方法的研究进展。     

Reconstruction of the rolling contact fatigue cracks in rails using X-ray computed tomography

Rolling contact fatigue (RCF) defects are associated with complex crack networks at the subsurface. A computed tomographic (CT) scanning technique has been developed to reconstruct the 3D geometry of the RCF cracks in the railhead. Sample rails having squats of different severities were taken from the Dutch railway network. Four specimens of different sizes were prepared and investigated with the CT scanner. The detailed procedures of the CT experiment and post-processing work were described. A sequence of high-quality X-ray images was collected during each scan. These 2D images were combined to construct the 3D visualization of the specimen. Various image processing tools were applied to extract and rebuild the internal crack geometries, thus allowing the crack networks to be differentiated from the bulk steel. For validation, the CT results were compared with metallographic observations of the rail surface for all the defects and the vertical section when needed. Discussions were made regarding the proper size of the rail samples and severity of the squats. According to the results, CT allows for a 3D visualization of RCF defects, providing high-quality data on the geometry of the internal cracks. By choosing the appropriate settings and specimen size, CT could accurately reconstruct the squat cracks at different growth stages. This research shows the potential of the CT technique as an intermediate detection and characterization tool among the methods for detecting macro cracks and those for characterizing micro/nano cracks. Finally, a practical specimen design and a detailed scanning procedure are proposed, based on the CT experiments performed in this research.     

Non-destructive testing in the high-temperature regime by using a magneto-optical film

The plane of a polarized light beam is rotated when the beam is transmitted through a magneto-optical film (MOF). Magnetic flux leakage (MFL) occurs around a crack when the specimen is magnetized and affects the magnetic domains. Therefore, a crack can be detected using a polarized lighting system and MOF. The crack detection ability depends on the domain width and saturation magnetization of the MOF. Also, crack detection at high temperatures is essential. The physical properties of the MOF at high temperatures were examined, and a nondestructive testing (NDT) method for detecting cracks at high temperatures was proposed in this paper.     

A fast method for rectangular crack sizes reconstruction in magnetic flux leakage testing

Magnetic flux leakage (MFL) testing is widely used to examine ferromagnetic materials. For the reason of estimating the sizes of cracks in metals is important in piping industries, a fast method based on particle swarm optimization algorithm is proposed for reconstructing the sizes of rectangular crack in this article. Considering the magnetic leakage field intensity is related to the air gap between the inspection specimen and the sensor, we give the reconstruction results in different lift-off values. Besides, the influence of different magnetic conditions to the reconstruction effectiveness has been investigated. The simulation results have shown the rapidity and accuracy of the proposed method.     

Composite magnetic flux leakage detection method for pipelines using alternating magnetic field excitation

Pipelines are an important transportation medium for petroleum and chemical products, but defects in the pipelines can present hidden dangers and affect the safe operation of the pipeline. The traditional pipeline magnetic flux leakage (MFL) scanning technique generally adopts the axial magnetization mode, which has increased the difficulty in detection and the possibility of missed detection of axial cracks. In this paper, a new composite MFL method using alternating magnetic field excitation is proposed for the detection of cracks in pipelines. The alternating magnetic field is first superimposed on the MFL magnetization field, which will form a parallel eddy current field perpendicular to the magnetization direction in the pipeline wall. The defects in the pipeline not only cause the flux leakage of the magnetization field, but also lead to the disturbance of the circumferential eddy current field. The disturbance signals can be picked up through a secondary induced magnetic field. Because the magnetic field and the eddy current field are orthogonal, the presented method can implement synchronous detection in two orthogonal directions to avoid missed detection caused by the crack orientation. A series of physical experiments are carried out in this paper. The results show that two orthogonal detection signals can be separated by a simple low pass filter. Therefore, with only one scan, the new detector can obtain the defect characteristics in the axial and circumferential directions to overcome the blind spot problem seen in traditional MFL detectors.