【作者】 张康；

【导师】 彭建平；

【作者基本信息】 西南交通大学 ， 物理学， 2018， 硕士

【摘要】 车轮作为机车走行部的关键部位,直接影响机车的安全运营。车轮在机车运行过程中与钢轨之间滚动接触作用使得车轮表面常萌生出滚动接触疲劳裂纹,裂纹的存在使得车轮的安全性和可靠性大大降低,且由于车轮长期处于恶劣的自然环境中,当裂纹中存在第三种介质对裂纹进行填充并造成裂纹闭合时,会降低裂纹的检出率,同时缺陷定量的难度也大大提高。基于此,文章采用涡流脉冲热成像检测方法针对车轮踏面闭合疲劳裂纹进行检测和研究,研究第三种介质对于裂纹检测的影响。本文的主要研究内容如下:首先对矩形线圈、亥姆霍兹线圈和磁轭线圈的激励场和激励特性进行了对比分析。并针对车轮弧形踏面设计了曲面型试块进行缺陷检测效率的对比。其次根据氧化致闭类疲劳裂纹建立了闭合裂纹的有限元模型。以开口裂纹为对照,针对缺陷的开口状态、尺寸及第三介质电磁属性等参数的变化,从涡流场和温度场两个角度分析了闭合裂纹检测特性。最后设计了闭合裂纹试块及相应的对比试块,基于现有的检测平台进行了实验验证。对于实验采集到的热响应序列从温度场的角度进行了一系列的分析:将开口裂纹作为对照,既分析了闭合裂纹尖端的温度幅值、走势、一阶导数;又基于等温线理论研究了缺陷区域的温度梯度,对缺陷特征进行了提取和分析,增强了缺陷特征,提高了缺陷检测效率。并将仿真和实验的结果进行了对比分析。本文通过以上三个方面对闭合裂纹涡流脉冲热成像检测进行了研究。通过对激励线圈特性进行分析为激励线圈的选择提供了理论依据。同时对闭合裂纹的涡流场和温度场进行了分析,为缺陷的定性和定量提供了基础。更多还原

【Abstract】 As the key part of the locomotive running part,the health condition of the wheels directly affect the safety of the locomotive.Rolling contact fatigue crack emerges at the surface of the wheels during the interaction between wheels and rail.The existence of the crack lower the safety and reliability of the wheels,with the wheels working in the harsh natural environment,cracks can be filled with third kinds of medium,leading to crack closure,which lower the probability of detection inevitably and thus enlarge the difficulty of defect quantification.Eddy current pulsed thermography is then employed to study the effect of third kinds of medium on the crack detection of wheel tread.The main contents of this thesis are as follows:First,the excitation characteristics of the rectangular coil,the Helmholtz coil and the yoke coil are compared and analyzed.A curved test block is designed according to the structure of wheel tread to study the defect detection efficiency.Secondly,a finite element model of closed crack is established based on the closed fatigue crack induced by oxidation.According to the change of the opening state,size and the electromagnetic properties of the third medium,the closed crack detection characteristics are analyzed from two aspects including the disturbance of both eddy current field and the temperature field.Finally,closed crack test block and corresponding contrast test block were designed,and the experimental verification was carried out based on the existing detection platform.A series of analysis of the thermal response sequence collected by the experiment is carried out.The temperature amplitude,the trend and the first derivative of the closed crack tip are analyzed,and the temperature gradient of the defect region is studied based on the isotherm theory,by which the defect characteristics are extracted and analyzed.The defect characteristics are enhanced and the defect detection efficiency is improved as well.The results of simulation and experiment are compared and analyzed.In this thesis,closed crack is detected by eddy current pulse thermography through three aspects.By analyzing the characteristics of the excitation coil,it provides a theoretical basis for the selection of the excitation coil.At the same time,the eddy current and temperature fields of closed cracks are analyzed,which provides a basis for qualitative and quantitative analysis of defects.更多还原