变厚度板壳结构中的非线性兰姆波

Interest in the propagation characteristics of nonlinear ultrasonic Lamb waves in plate and shell structures continues to grow in recent years. By combining the advantages of guided waves and nonlinear ultrasonic waves, nonlinear Lamb wave testing techniques are widely applied in the evaluation of early fatigue damages of plate and shell structures. Comparing with constant-thickness, variable-thickness plate and shell structures are more practical in engineering. However, due to the wave scattering and mode conversion problems, Lamb waves in variable-thickness plate and shell structures were not fully investigated, and the nonlinear problems were even rarely reported. The propagation, scattering and mode conversion of Lamb waves in variable-thickness plate and shell structures will be studied, the existing conditions and excitation efficiency for nonlinear Lamb waves will be analyzed, the cumulative nonlinear Lamb wave modes will be searched and the relationship between their cumulative properties and thickness variation will be studied. Furthermore, the impact that micro-damage has on nonlinear Lamb waves, and nondestructive evaluation method of micro-damage by nonlinear Lamb waves will be investigated. The work will boost the development of nonlinear Lamb wave theories, as well as provide guidelines for practical applications of nondestructive evaluation techniques by nonlinear Lamb waves.

近年来，板壳结构中非线性兰姆波的传播特征得到了较多关注。由于兼备了导波与非线性超声波的优点，非线性兰姆波检测方法在等厚度板壳结构的早期疲劳损伤评价中得到诸多应用。相比于等厚度板壳，变厚度板壳往往更接近实际工程结构。然而，由于存在散射和模式转换等复杂问题，变厚度板壳结构中的兰姆波并未得到深入研究，其中的非线性声学问题则更是鲜有报道。本项目拟研究变厚度板壳结构中兰姆波的传播、散射和模式转换问题，分析非线性兰姆波存在的条件和激发效率问题，寻找具有累积效应的非线性兰姆波模式并分析其增长特征与厚度变化的关系，进一步分析结构微损伤对非线性兰姆波的影响，研究利用非线性兰姆波进行微损伤评价的方法。本项目的工作一方面可以丰富和发展非线性兰姆波理论，另一方面可以为非线性兰姆波无损评价提供更直接的技术指导。

近年来，板壳结构中非线性兰姆波的传播特征得到了较多关注。由于兼备了导波与非线性超声波的优点，在等厚度板壳结构的早期疲劳损伤评价和材料健康监测等方面得到诸多应用。相比于等厚度板壳，变厚度板壳往往更接近实际工程结构。然而，由于存在散射和模式转换等复杂问题，变厚度板壳结构中的兰姆波并未得到深入研究，其中的非线性声学问题则更是鲜有报道。本项目研究了变厚度板壳结构中兰姆波的传播、散射和模式转换问题。分析了在厚度缓慢变化下非线性兰姆波的产生和传播规律，讨论了在考虑声波衰减的情况下非线性兰姆波传播效应的变化，提出了理论的适用范围。研究了非线性兰姆波在阶梯板中传播的特性，明确了阶梯板的存在对非线性兰姆波的传播的影响。建立了阶梯板厚度差与各个模态和频率的非线性兰姆波能量分配比例的关系。设计了一种基于激光多普勒振动仪的透明固体弹性波测量装置，获得了比压电换能器更高的灵敏度和更完整的声场信息，实现了各个兰姆波模态的幅值和相位随传播距离变化的连续测量。