基于Lamb波应用的时间反转非线性弹性检测与成像研究

Now, nonlinear acoustic technique has been obtained more and more applications in material nondestructive testing and imaging. Recent researches prove that the combination of Nonlinear Elastic Wave Spectroscopy (NEWS) and Time Reversal Acoustic (TRA) methods can effectively improve the sensitivity and precision of damage detection, however, scarcely researches of Lamb waves application in this combination have been done and presented. The research of Lamb waves in the combination of NEWS and TRA for material defect detection and imaging will be done in this project. The mode transmission, time reversal technique and nonlinear properties of Lamb waves will be investigated by means of numerical simulations and experiments research at the same time. In order to profoundly understand the interaction between the nonlinearity of material and Time Reversal Acoustic (TRA), the research of invariance influence of the TRA introduced by material attenuation will be carried out. In our experiments of Lamb waves, two different kinds of combination applications of NEWS and TR (TR-NEWS and NEWS-TR) will be expanded in material crack detection and imaging. Moreover, the other time reversal techniques, e.g., Inverse Filter (IF) and 1 Bit proceeding (1B) methods, will replace the TR and make some different kinds of combinations with NEWS technique for improving the quality of Lamb waves imaging. Finally, the aim of our research project is to realize the nonlinear time reversal detection and imaging based on Lamb waves application and to enrich and develop nonlinear theory of Lamb waves.

非线性声学在材料无损检测及成像中已经获得越来越多的应用。前期的研究结果表明，非线性弹性波谱（NEWS）技术和时间反转（TR）技术的结合可以有效提高缺陷检测的灵敏度和精度，但这两者的结合在Lamb波的检测应用中鲜有介绍。本课题就Lamb波与TR及NEWS技术在缺陷检测及成像中的结合应用展开研究。课题组拟采用实验研究和数值仿真计算相结合的研究方法，对Lamb波的模态转换、时间反转特性、非线性谐波特性等做深入研究；通过对时间反转（TR）技术与非线性弹性波谱（NEWS）技术的两种不同结合方式TR-NEWS及NEWS-TR做对比分析，并对不同的时间反转声学技术：经典时间反转（TR）、反向滤波（IF）及1位（1B）处理技术进行应用，以探讨不同的时间反转技术在Lamb波的非线性裂纹检测及成像中的应用问题，进而完善和发展Lamb波非线性检测及成像理论。

本课题针对Lamb波的非线性缺陷检测与成像、裂纹检测及其方向识别展开研究，课题结合以时间反转声学及非线性声学的运用实现了对固体板状介质中的损伤及缺陷识别。主要的研究内容包括：1. 裂纹缺陷与非线性Lamb波相互作用关系的分析研究；2. 基于时间反转的非线性Lamb波缺陷检测与成像技术研究；3. 混频激发的非线性Lamb波微裂纹方向识别研究。.通过本课题的研究，取得如下研究结果：1. 通过频谱分析法的应用，得出非线性Lamb波信号对三维板中不同尺寸的裂纹具有不同的反应灵敏度，非线性Lamb波信号会随着裂纹长度或高度的增加而增强，会随着裂纹厚度的增加而变弱；2. 通过混频激发技术的应用，得出非线性Lamb波对薄的微裂纹和窄的分层缺陷具有更高的敏感性和更好的灵敏度；3. 通过将时间反转技术和层析成像技术相结合，实现了对损伤的检测与成像，且此两种方法的结合极大提高了损伤检测的效率和成像质量，有效降低了检测的误差；4. 通过时间反转技术和混频激发技术的结合应用，实现对非线性Lamb波信号的提取，并利用该非线性信号完成了对裂纹指向性的识别，得出裂纹方向与Lamb波最大前向散射点和最小后向散射点的连线相垂直。.基于本项目的研究，课题组对 Lamb 波非线性信号的提取方法进行了分析，实现在铝板及复合材料介质中Lamb波信号激励后的时间反转，推动了非线性声学技术在 Lamb 波检测成像中的应用，为 Lamb 波非线性检测技术及理论的发展做出贡献。