激光超声波检测金属表面缺陷的理论及实验研究

【作者】 韩昌佩；

【导师】 沈中华；

【作者基本信息】 南京理工大学 ， 光学， 2012， 硕士

【摘要】 本文从实验及有限元方法两方面展开对激光超声缺陷检测的研究,主要提出一些判断缺陷位置、尺寸等信息的方法。本文内容主要从如下几个方面展开分析讨论：采用有限元方法模拟了激光线源激发铝板表面超声波的物理过程。进而分析了表面波与表面矩形缺陷的相互作用及存在缺陷时的各种超声模式；最后提取表面位移信号分析缺陷对激光超声的影响,并反演缺陷位置、尺寸等相关信息。采用PVDF压电传感器接收超声信号及指向性优越的激光线源作为超声波激发源建立激光超声缺陷检测实验平台。应用该平台研究了接收器与激发源同侧及异侧时铝板内出现的各种超声模式以及由于缺陷的存在而导致表面超声信号的变化规律。实验及模拟部分均分析了缺陷对表面超声信号的影响,主要从反射波及透射波两方面定量讨论了超声信号与缺陷的关系。提出了反射信号中双峰值瑞利波峰峰值、震荡区域时间间隔及透射信号中双峰值瑞利波峰峰值、时间展宽及掠面纵波峰峰值随缺陷深度的变化规律。并对不同缺陷深度的反射及透射波信号进行了频谱分析,总结出缺陷对反射及透射超声波信号的选频作用的结论。本文的研究结果可为金属表面缺陷的定量检测研究提供实验依据。也为激光超声无损检测技术的发展提供理论依据。更多还原

【Abstract】 In this paper, we mainly used experiments and finite element method (FEM) to research the laser ultrasonic flaw detection and provided some methods to investigate the location, size and some other information of the flaw. The main content of this work are listed as follows:FEM was used to simulate the physical process of surface ultrasonic which excited by laser line source on aluminum plate. Further, some analysis was made on interactions between the surface ultrasonic and surface rectangular flaw, and the various ultrasonic model when the flaw existed; Finally, we extract the surface displacement signal to analyze the affect of laser ultrasonic produced by flaws, at the same time, inverse the flaw location, size and other relevant information.We established the flaw detecting experimental platform which used the PVDF piezoelectric sensor to receive ultrasonic signal and the laser line source to excitated the laser ultrasonic. Application of the platform, we studied the various ultrasound modes and the relationship between ultrasonic and flaw under the receiver and the excitation source place the same or different side.In this paper, both experiments and numerical simulations analyzed the influence of flaws to the surface ultrasonic signal. The relation between the ultrasonic signal and flaws was discussed from two respects:one is reflected wave, the other is transmission wave. We put forward some characters of reflection signal such as peak to peak value and time indifference of the Rayleigh wave of the double peak region. Some characters of transmissive wave were also given such as time broadening, peak to peak value of the double peak region. And we put forward same characters for the surface skimming longitudinal waves. Finally, we analysis spectrums of the reflective and transmissive wave with different flaw depth, we summarize the conclusion as follows the defects have frequency effect to the reflection and transmission of ultrasonic signal.This research result will provide an experimental basis for laser ultrasonic detection of metal surface flaw, and theoretical basis for the technology of ultrasonic nondestructive testing.更多还原