高能光纤相控阵激光超声检查方法及在结构内部缺陷检测中的应用研究

Ultrasonic testing method (UT) has been widely applied in aerospace, nuclear energy and some other important industries. Laser ultrasonic testing (LUT) is a very promising new UT method due to its outstanding advantages of high resolution, good accessibility, and remote feature which the traditional UT method doesn’t own. However, as the low signal strength in thermos-elastic regime and low defect detecting ability (especially for inner defect in structures), the application of LUT method in industry is quite limited presently. In order to promote the theoretical development and industry application of the LUT method, in this project, the development of phased-array LUT method with using a high-channel and high-energy fiber delivery system is proposed to enhance the generation efficiency and signal strength of laser ultrasound. That can be used to solve the problem of quantitatively measurement of the inner defects in metallic structures with LUT method. The main contents of this project include: (1) Development of FPA laser sources with high channels and high energy; (2) 3D theory model of PA laser ultrasound field in thermoelastic regime; (3) Development of high-efficiency phased array focusing method and signal receiving /processing method; (4) The methods of measurement of inner defects in metallic structures with FPA LUT method. The research results of this project will significantly improve the performance of LUT method, and provide a more effective remote NDT method and system for many important equipment.

超声检测方法广泛应用于航空航天、核能等重要装备的安全检测，激光超声具有传统超声方法不具备的高分辨、可达性好、可非接触远距离检测等突出优点，是一种非常有潜力的新型超声检测技术。目前激光超声检测方法由于信号弱、对缺陷（特别是结构内部缺陷）检测能力低等问题，限制了其工业实际应用。为促进激光超声检测方法的理论发展和工业应用，本项目拟开发基于高能高通道光纤传输系统的相控阵列激光超声方法，有效增强激光超声的激发效率和信号强度，解决金属结构内部缺陷激光超声定量无损检测难题。项目主要研究内容包括：（1）基于光纤传输的相控阵列激光源的高能化及高通道化；（2）相控阵激光超声的三维声场分布特征分析；（3）高效激光阵列聚焦方法和信号接收处理方法开发；（4）基于所开发相控阵激光超声技术的金属结构内部缺陷定量检测方法。项目研究成果可显著提高激光超声检测性能，为重要装备提供更加有效的远距离无损检测方法和系统。

激光超声由于具有高分辨、可达性好、非接触和远距离检测等突出优点，是一种非常有潜力的新型超声检测方法。本项目针对目前激光超声热弹模式下检测信号弱，对金属结构内部缺陷检测能力较低等问题，研究和开发了一种基于高能光纤阵列束传输的全光学型相控阵激光超声检测方法，有效提高了激光超声的检测能力，课题组完成了项目预期研究内容和目标。取得主要研究成果如下：1）应用新型大口径高能光纤，设计和开发了一种基于单一脉冲激光器的7通道高能相控阵列激光源，实现了光纤束传输的相控阵列激光源的高能化和高通道化。此外，设计和开发了一种专用聚焦镜头，实现了对经光纤束传输的激光在被测试件上的远距离聚焦和线形阵列排布。最后结合实验室已有的激光超声干涉仪，完成了基于高能光纤束传输的全光学型相控阵激光超声检测系统的开发；2）在现有二维激光超声声场分布理论模型基础上，建立了激光激发超声波三维声场理论模型，在此基础上结合数值计算方法，分析了激光阵列参数对超声聚焦和传播的影响，进一步对实验系统进行了优化和扩展，提高了其使用性能；3）提出了一种圆弧形激光激励空间调制的激光超声点聚焦增强方法，研究了基于点聚焦激光超声体波的金属试件内部缺陷检测方法，实现了对金属试件内部不同缺陷的检测，提高了激光超声对金属内部缺陷的检测能力和分辨率。4）利用所开发的光纤相控阵激光超声检测系统，对金属试件底面不同尺寸裂纹缺陷进行了检测和定量评价实验研究，实现了相控阵线聚焦激光超声对大厚度金属试件内部裂纹的完全非接触、高精度定量无损检测；