车轴压装界面超声响应机理及缺陷探测研究

The security of the axle is the key problem which must be solved for the high-speed and heavy-haul railway. Therefore, to improve the ultrasonic detection ability of the axle press-fit area which is the key part of the axle becomes a problem demanding prompt solutions. This project intends to reveal the ultrasonic propagation characteristic on axle press-fit interface through experiments, theoretical analysis and simulation, and then to study effective method improving detection ability of the axle press-fit area. First of all, through the system experimental study, the interface and the defect echo characteristic on 'solid-gas' interface before press-fit and partially contacting 'solid-solid' interface after press-fit will be gotten. Then, through the study of axle stress distribution after press-fit, 'solid-solid' interface micro model and ultrasonic propagation characteristic, the ultrasonic propagation physical model at the axle press-fit interface with and without defects will be established. This project will do further research on the self-focusing phased array probe based on the sound field theory and the press-fit interface reflection signal suppression algorithm based on the time-frequency analysis theory. Through the above research, the ultrasonic wave response mechanism of the 'solid-solid' interface will be understood systematically and comprehensively, and then the ultrasonic propagation theoretical model of the axle press-fit interface will be established, based on this the improvement of defect detection ability and the interface reflection signal suppression methods will be studied, at last the improvement suggestions for existing technology will be put forward in this project.

车轴安全是高速、重载铁路运营必须解决的关键问题。提升车轴关键部位——轮座压装部的超声波探伤能力已成为亟待解决的问题。本项目拟通过试验、理论分析、计算仿真揭示超声波在车轴压装界面处的传播特性，研究车轴压装界面处缺陷探测能力提升的有效方法。首先通过系统试验研究掌握车轴压装前‘固-气’界面与压装后局部接触‘固-固’界面超声波缺陷反射及界面反射波形特征。其次，通过研究车轴压装车轮后的应力分布、‘固-固’界面微观模型、超声波传播特性，建立存在缺陷的车轴压装界面超声波传播物理模型。本项目还将研究基于声场理论的自聚焦相控阵探头以及基于时频分析理论的车轴压装界面反射信号抑制处理。通过上述研究，系统全面认识车轴压装界面处超声波分别对缺陷和‘固-固’界面的响应机理，进而建立车轴压装界面处超声波传播理论模型，在此基础上研究提高缺陷探测能力、抑制界面反射信号的措施，最后提出既有工艺改进建议。

步入21世纪，世界铁路蓬勃发展，我国更是规划了宏伟的轨道交通蓝图。车轴作为铁路运营的关键部件，长期经受疲劳载荷作用，易在应力集中区域萌生疲劳裂纹，危及行车安全。对在役车轴定期实施无损探伤能有效防止疲劳裂纹导致的断轴事故。本课题旨在研究车轴疲劳裂纹超声波探伤技术及工艺，提升车轴压装部位的缺陷检测性能，从而保障车轴运用安全性。.本课题系统研究了国内外不同检修工艺、不同工况下的实心轴和空心轴超声波探伤技术，设计并优化了相控阵超声技术从轴身和轴端耦合探伤的工艺；通过仿真设计和对比试验，研究采用内凹面晶片自聚焦相控阵超声探头提高车轴缺陷探测性能，压装部缺陷检测平均灵敏度提高14.7dB，检出缺陷信噪比平均提高8.3dB。经分析压装界面反射波成因，采用空域数字图像处理方法实现图像增强和滤除特定的噪声；根据压装部界面反射波与缺陷反射波的特征，提出并优化基于形态特征滤波的小波阈值法去噪和各向异性扩散去噪算法；最后，试验研究形成最优滤波组合方案，经人工裂纹样板轮对和实物轮对测试，缺陷波幅平均只削弱0.41dB，压装带波幅均值削弱平均力度达6.07dB，证明该算法组合能够在有效保留缺陷信息的前提下削弱轮座压装界面反射波，从而提高缺陷检出信噪比、优化超声成像质量，具有良好的适用性。