结构疲劳裂纹的非线性波动特征及其概率诊断与监测

Engineering structures experience continuous accumulation of fatigue cracks and deteriorate over their lifespans, potentially leading to catastrophic consequences. This concern has entailed substantial research efforts towards detection of fatigue cracks at initial stages. The majority of current detection methodologies rely on linear macroscopic changes in elastic wave scattering (e.g., reflection, transmission or mode conversion). However, initial fatigue cracks at microscopic levels present highly nonlinear characteristics which may not be well evidenced in these linear macroscopic changes. By exploring the higher-order acoustical nonlinearities of elastic waves modulated by fatigue cracks, a characterization approach, in conjunction with the use of an active PZT sensor network, will be established, with the particular capacity of evaluating multiple fatigue cracks at a quantitative level (including the co-presence of multiple cracks, and their individual locations and severities). The research will unveil the fundamental mechanism of the modulation of micro-fatigue cracks on higher-order nonlinearities of elastic waves; develop an active PZT sensor network, rather than using traditional ultrasound transducers, for the generation and acquisition of nonlinearities of elastic waves, with a purpose of structural health monitoring; configure a novel damage index to quantitatively characterize fatigue cracks; establish a probability-based diagnostic imaging algorithm; and experimentally validate the proposed approach. In particular, the first two tasks are the key research contents in this project. The approach is expected to contribute to fundamental understanding of modulation mechanism of fatigue damage on elastic waves, and development of cost-effective structural health monitoring approaches taking advantage of acoustical nonlinearities of elastic waves.

疲劳裂纹的萌生、扩展、贯通会诱发工程结构的灾害性事故。将弹性波用于疲 劳裂纹诊断是一个在国内外得到广泛关注的课题。目前，基于波动理论的疲劳裂纹诊断大多位于线性范畴，即利用波的反射、透射、模态转变等宏观线性特征。但初始状态的疲劳裂纹往往不足以引起这些线性特征的改变。该研究以疲劳裂纹的介质非线性为基点，从介质非线性引发高频弹性波的非线性波动特征为切入点，对主动、在线、定量、可视化的疲劳裂纹诊断中的关键理论与方法展开攻关。该研究将定量揭示疲劳裂纹对弹性波的非线性调制机制；分析采用压电晶片而非传统探头捕获非线性波动特征的机理，为实现在线结构健康监测创造条件；基于二倍频非线性波动特征，构建疲劳损伤特征因子；建立压电主动传感网络支持的概率检测模式；开展丰富的物理模型试验，对所提理论与方法进行检验。其中，前两项机理研究为该课题的首要攻关内容。预期成果将有力提升现有理论与方法水平，并为产生有生命力的疲劳裂纹诊断与主动监测提供科学依据。

该国家自然基金课题自2014年1月执行以来，通过四年的深入研究，目前已经顺利结题。课题组按照原计划顺利履行了各项研究步骤。在遵循时间节点的情况下，取得了所有预期的研究成果。课题研究内容无改动。. 在研究当中，课题组以疲劳裂纹的萌生、扩展、贯通会诱发工程结构的灾害性事故为研究背景，针对目前基于波动理论疲劳裂纹诊断大多位于线性范畴的研究现状，以疲劳裂纹的介质非线性为基点，从介质非线性引发高频弹性波的非线性波动特征为切入点，对主动、在线、定量、可视化的疲劳裂纹诊断中的关键理论与方法展开了攻关。通过研究，定量地揭示了疲劳裂纹对弹性波的非线性调制机制；分析了采用压电晶片而非传统探头捕获非线性波动特征的机理；实现了在线结构健康监测；基于二倍频非线性波动特征，构建了疲劳损伤特征因子；建立了压电主动传感网络支持的概率检测模式；并开展了丰富的物理模型试验，对所提理论与方法进行了检验。. 在四年的时间里，围绕以上的研究内容，课题组在该领域顶级SCI期刊上发表了一共15篇高水准文章，并在该领域主要国际会议上发表了16篇文章（均被会议论文集收录）。所有文章均清楚致谢了该国家自然基金项目。.在课题执行的四年中，课题组获取了大量的数据。这些数据对将有力提升现有基于波动理论的疲劳裂纹诊断理论与方法研究水平，并为产生有生命力的疲劳裂纹诊断与主动监测提供科学依据。