基于兰姆波共线混叠的微损伤检测方法

In aircraft and aerospace, nuclear power industries, nondestructive evaluation and testing of material degradation or micro-damages in an early-stage is essential for the maintenance of the safety-critical structures. Nonlinear ultrasonic technique has been accepted as a potential tool to characterize the material micro-structural change. This project is based on nonlinear wave mechanics and combined with the features and principle of Lamb wave propagation, to investigate the collinear wave mixing phenomenon of two different Lamb wave modes in a nonlinear plate-like structure, the two wave modes have the same propagation direction and with different frequencies. It aims to studying the generation and mechanism of the acoustic nonlinear response of collinear Lamb wave mixing in the specimens with damaged induced nonlinearity. The objective of this research is to explore nonlinear Lamb wave theory based on collinear wave mixing and to propose a nonlinear Lamb wave inspection and evaluation approach by collinear wave mixing . It is to develop a nonlinear ultrasonic nondestructive testing technique which can be used to identify the nonlinear sources, and locate the damaged induced nonlinear response in this project. The investigation of collinear Lamb wave mixing-based nonlinear ultrasonic detection has important theoretical value and engineering demanding needs for the inspection and location of material micro-damages.

在航空航天、核电工业中，一些重要关键装备构件的微损伤或材料性能退化需要及时的检测和评估以保障它们的安全运行。非线性超声检测方法是表征材料微观组织结构变化的有效手段。本项目基于非线性波动理论，结合兰姆波传播特点和规律，研究两个相同传播方向、不同频率的兰姆波模式在非线性介质材料中混叠传播的非线性响应规律。分析波束共线混叠后声学非线性响应与材料微观缺陷的关系。探索基于波束共线混叠的非线性兰姆波检测理论，开发基于兰姆波波束混叠的非线性超声检测方法。通过对本课题的研究，建立一种可以有效描述非线性来源、并能判断发生非线性响应位置的微损伤检测技术。对材料微损伤的检测和定位具有十分重要的理论研究价值和工程应用需求。

针对工业结构中的微损伤早期检测需求, 本项目考虑到非线性超声检测方法对微损伤检测的敏感性，结合兰姆波的传播特点与规律，研究了兰姆波波束混叠非线性响应特征，并用于检测和评估金属薄板的微损伤。研究的主要研究内容包括：兰姆波共线混叠非线性响应的机理研究和兰姆波共线混叠传播的模型构建及实验研究。项目研究获得重要结果如下：（1）开发出一套兰姆波在薄板结构中传播的频散分析软件，通过本软件可以确定合适的兰姆波模式组合。选取的兰姆波模式组合其波束混叠可以诱发强烈的混叠非线性响应。（2）初步建立了波束共线混叠的非线性兰姆波传播理论模型，在理论模型中，给出了兰姆波共线混叠后的非线性项的一般表达式。（3）在理论模型的指导下，实验观察出了兰姆波共线混叠的非线性响应现象，实验观察与理论预测有较好的一致性。（4）开发出了基于兰姆波共线混叠的非线性兰姆波检测技术，此技术解决了目前基于高次谐波法的非线性兰姆波技术无法有效区分非线性源，无法判断损伤位置的技术难题。本项目的研究为提高非线性兰姆波检测技术的可靠性、精确性提供一个新的方法。利用这项技术可以实现对关键结构件的非结构健康监测与寿命评估。