轮轨疲劳裂纹的涡流脉冲热响应机理与量化检测研究

The safety of the rail and wheel is an issue which must be solved in the high-speed and heavy-haul railway. Therefore, to improve the capability of fatigue status monitoring in rail/wheel, especial the initial fatigue closure crack which is the key source of rail/wheel damage. This project intends to reveal the electromagnetic induction and thermography mechanism on fatigue closure crack in rail/wheel, research on fast measurement and monitoring these closure cracks’ state (closing or opening) and quantification through theoretical study, module and simulation, experimental study. Based on that, it hopes to improve the fatigue closure crack monitoring capability. First of all, according to the external loading and residual stress distribution on fatigue crack area in rail/wheel, study the eddy current distribution and thermal propagation around the closure crack using theoretical and numerical module ways; then, study the influence of filler between crack which is equivalent as low conductance model, understand the fast measurement mechanism and quantification evaluation of fatigue closure crack using eddy current pulsed thermography. The project will be employed to study wheel fatigue crack detection in high-speed railway, using the uniform field exciting to heat the material, extracting and locating the fatigue crack on wheel tread through thermography image sequences, classing the default and realize the qualification inspection and evaluation for real wheel.

轮轨安全是高速、重载铁路运营必须解决的关键问题。高效掌握轮轨的疲劳损伤状态，尤其疲劳早期的闭合疲劳裂纹的探测能力成为亟待解决的关键问题。本项目拟通过理论分析、建模仿真和试验对比分析揭示轮轨疲劳裂纹在闭合及张开状态下的电磁热作用机理，研究电磁热特征提取和量化方法思路，提升疲劳裂纹状态的检测和量化能力。首先基于负载或残余应力分布对疲劳裂纹的闭合稳态性研究，理论和建模分析闭合裂纹的涡流分布特征和热传导过程；研究轮轨裂纹的填充物质影响，基于弱电导缺陷模型开展涡流脉冲热成像快速检测机理和量化评估；最后针对车轮踏面的前期疲劳损伤，开展弧形踏面均匀场激励优化、疲劳缺陷图像算法优化等基础应用研究,实现对车轮滚动接触区域的疲劳裂纹定量检测和评估。

轮轨疲劳裂纹的探测能力在保障铁路运输安全运营中起着关键作用。传统无损检测方法对疲劳早期的闭合疲劳裂纹表征中存在局限，本项目采用涡流热成像检测方法，结合理论研究、建模仿真和试验验证等手段，系统分析了轮轨疲劳裂纹的电-磁-热作用机理。主要研究内容包括：1）设计了疲劳裂纹缺陷—复合型角度裂纹模型，研究了裂纹侧壁接触和裂纹区域填充所致的裂纹状态改变与电磁热作用机理，进一步完善了电磁激励热成像疲劳裂纹检测模型；2）研究轮轨接触面滚动疲劳裂纹检测及量化方法，结合张量分解算法等提取分离缺陷热响应信息，探究电磁热响应规律，实现疲劳微裂纹定位和评估；3）先后研制了适用于铁路领域的动态车轮、钢轨动态检测实验系统，验证了轮轨疲劳裂纹检测和量化能力。重要成果包括：1）针对疲劳裂纹侧壁局部接触导致的量化困难问题，构建出单点接触闭合弱电导缺陷模型，研究裂纹侧壁接触情况下的电-磁-热分布物理特征，并实现接触区域的深度量化检测；2）结合基于矩阵分解的图像增强方法强化缺陷特征，扩展了热序列图像数据分析技术；3）确立了涡流分布和热扩散过程与空间热序列特征的扰动关系，实现区域多裂纹检测量化；4）完成了铁路车轮弧形踏面均匀场激励模型优化，在此基础上研制了在役车轮检测系统，实现65mm/s转轮速度下0.2mm宽的横向裂纹进行检测；5）研制了动态钢轨巡检实验系统，通过实验验证，可在5km/h速度下对深度范围为0.35mm-5mm的闭合裂纹进行检测。科学与应用意义：相关研究成果针对铁路轮轨疲劳裂纹失效机理及其闭合状态建模研究，对疲劳裂纹的电磁热多物理场表征，对轮对和钢轨早期缺陷检测具有重要的理论价值，对提高轮轨疲劳裂纹的检测和量化评估具有很好的工程应用价值。