金属表面缺陷和钢轨踏面残余应力的激光超声无损检测研究

发布时间：2018-03-04 12:11

本文选题：双激光线源　切入点：横波会聚效应　出处：《北京交通大学》2016年博士论文　论文类型：学位论文

【摘要】：无损检测技术是指在非损坏的条件下对各种材料、工件进行检测,以及对服役期间的产品性能进行评估的技术,激光超声作为一种新兴的检测手段,因其拥有传统超声检测无法比拟的优点,受到了无损检测界的广泛关注。随着我国铁路的发展,对钢轨的质量检测要求也随之提高,其中残余应力对钢轨的疲劳性能的影响最为明显,是工件产生裂纹的重要原因。本文利用双激光线源激发超声波,从数值模拟和实验两方面研究了双激光线源扫描检测金属板材表面缺陷的机理,并搭建实验系统研究了钢轨踏面残余应力的分布。论文主要的研究工作如下:1.提出了一种采用双激光线源激发超声波的方法。利用横波在双激光线源对称轴处产生的会聚效应,有效的提高了热弹机制下超声波的激发效率。分别采用有限元方法及实验手段研究了横波的会聚效应、双线源间距对横波会聚效应的影响,实验结果与数值结果相符合。2.提出了一种采用扫描双激光线源探测金属表面缺陷的方法。应用有限元方法对横波波束与表面缺陷的相互作用过程进行模拟,模拟结果表明采用双激光线源检测金属表面缺陷的方法可以改善探测端信号的信噪比,对缺陷长度和方向的检测更加准确。3.搭建了一套扫描双激光线源探测钢板表面缺陷的实验系统。实验中采用双激光线源与TEMPO激光超声探测仪同步扫描,实现超声波的激发和接收。实验结果证明扫描双激光线源法是一种非接触式、非破坏、高效和高信噪比的金属表面缺陷的检测方法。4.搭建了一套钢轨踏面残余应力分布的非接触式激光超声探测系统。利用Nd:YAG脉冲激光器在钢轨踏面激发声表面波,TEMPO激光超声探测仪作为声表面波的接收装置,得到相邻探测处两个声表面波之间的传播时间差;基于声表面波的声弹性理论,测得了新轨和旧轨踏面中部以及外侧的应力分布。分析了声表面波传播声程和钢轨表面粗糙度对测量结果的影响,为准确检测钢轨踏面残余应力提供了基础。
[Abstract]:Non-destructive testing (NDT) technology refers to the testing of various materials and workpieces under non-damaged conditions, as well as the evaluation of the performance of products during service. Laser ultrasound is a new method of testing. With the development of railway in our country, the requirement of rail quality testing has been improved with the development of railway in our country because of its unparalleled advantages compared with traditional ultrasonic testing, and it has received extensive attention in the field of nondestructive testing. The influence of residual stress on the fatigue performance of rail is the most obvious, which is an important reason for the crack of workpiece. In this paper, the ultrasonic wave is excited by double laser line source. In this paper, the mechanism of double laser linear source scanning for detecting the surface defects of metal sheet is studied from the aspects of numerical simulation and experiment. The main research work of this paper is as follows: 1. A method is proposed to excite the ultrasonic wave by using the double laser line source. The convergence effect of the transverse wave at the symmetrical axis of the double laser line source is used. The efficiency of ultrasonic wave excitation under thermoelastic mechanism is improved effectively. The convergence effect of shear wave and the influence of the distance between two lines on the convergence effect of shear wave are studied by finite element method and experimental method respectively. The experimental results are in agreement with the numerical results. 2. A method of detecting metal surface defects by scanning double laser wire source is proposed. The interaction process of shear wave beam and surface defects is simulated by finite element method. The simulation results show that the signal-to-noise ratio (SNR) of the detected signal can be improved by using the dual-laser wire source to detect metal surface defects. The detection of defect length and direction is more accurate. 3. An experimental system for detecting surface defects of steel plate by scanning double laser wire source is built. In the experiment, double laser line source and TEMPO laser ultrasonic detector are used to scan synchronously. The experimental results show that the scanning double laser line source method is a non-contact and non-destructive method. High efficiency and high signal-to-noise ratio metal surface defect detection method .4.A non-contact laser ultrasonic detection system for residual stress distribution on rail tread is set up. Surface acoustic wave (tempo) excitation is induced by Nd:YAG pulse laser on rail tread. The optical ultrasonic detector is used as the receiving device of saw, The time difference between two surface acoustic waves at adjacent detection points is obtained, and based on the acoustic elastic theory of surface acoustic waves, The stress distribution in the middle and outside of the new and old rail tread is measured. The influence of surface acoustic wave propagation and rail surface roughness on the measured results is analyzed, which provides a basis for accurate detection of residual stress on rail tread.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG115.28;TN249

【引证文献】