金属材料内部亚毫米多缺陷定位与定量的激光超声横波阴影交叉检测方法研究

As a new noncontact ultrasonic nondestructive testing technique, the laser ultrasound technique has a great application prospect in the field of automatic intelligent detection in the new industrial era. Based on the amplitude changes and arrival time of the scattering ultrasonic waves from defects, the existing laser ultrasonic method is usually used for internal defects detection of materials. But when the diameter of internal defect is smaller than 1 millimeter, the signal-to-noise ratio of the scattering wave is low, and it is difficult to distinguish and quantify the internal multiple defects accurately. This project proposes a shadow crossing detection method based on laser ultrasonic shear wave. We study the sound field distributions of the laser ultrasonic shear waves. Three waves, which are the oblique transmission shear wave, the incident and reflected shear waves from the undersurface, are used for inspecting internal submillimeter defects from three directions. According to the interaction mechanism between defects and shear wave, the quantitative relationship among the size and location of defects and the time delay and attenuation position of shear waves are got. The path crossing point of the three waves are used for locating the internal defect, and the time delays of shear waves are used for quantifying the defects accurately. Through the study of this project, the internal multiple defects in metals can be located and quantified by using the shadow-crossing method. The method improves the accuracy of testing internal submillimeter defects and promotes development of the laser ultrasonic technology in the industrial nondestructive testing field.

激光超声技术作为一种新兴的非接触超声无损检测技术，在新工业时代的自动化智能化检测领域具有巨大的应用前景。现有的激光超声检测方法主要依据散射超声波的幅值变化和到达时间来检测材料内部缺陷，但在检测金属材料中的亚毫米缺陷方面还存在信噪比低、难以准确区分和定量内部多重缺陷等不足。本项目提出了一种基于激光超声横波的阴影交叉检测方法，通过研究激光超声横波的声场分布规律，利用斜透射横波、底面入射和反射横波从三个方向同时对内部亚毫米多缺陷进行检测。通过研究缺陷与横波的相互作用机理，探明缺陷尺寸和位置与透射横波幅值、波前时延以及衰减位置的定量关系，依据三个方向横波在缺陷衰减位置处的路径交叉点来实现内部缺陷的准确定位，并利用横波时延来准确定量。通过本项目的研究可以实现金属材料内部多缺陷的定位和定量检测，提高激光超声检测内部亚毫米缺陷的准确性，对推动激光超声技术在工业无损检测领域的发展具有重要意义。

针对金属材料中的亚毫米多缺陷，本项目提出了一种基于激光超声透射横波和底面反射横波的阴影交叉检测方法来对内部缺陷进行定量和定位检测。首先，通过理论、仿真计算结合实验，系统研究了激光超声横波的高效激发机理，掌握了横波在金属材料中的激发与传播特性规律。然后，研究了横波与内部缺陷相互作用的机理，掌握了横波与缺陷作用过程中的反射、透射、模式转换波的传播规律，以及作用后的横波声场分布，提出并证实了基于透射波前时延理论的内部缺陷定量检测方法。最后，构建了可实现激光超声透射横波和底面反射横波的阴影交叉检测的实验装置，分别采用双阴影交叉法和多阴影交叉法对铝合金试样中的亚毫米单缺陷和多缺陷进行了检测，结果表明，阴影交叉法结合透射时延方法可以实现金属材料内部亚毫米多缺陷的定量和定位检测。本项目的研究有效改善了了内部亚毫米多缺陷位置重合对激光超声检测的干扰问题，对推动激光超声技术在工业无损检测领域的发展具有重要意义。.