Lamb wave spectral methods are one candidate to characterize invisible damages in composite structures. Unfortunately, multiple reflections resulting from geometric boundaries could distort the Lamb wave spectrum, which may cover the important signatures concerning structural integrity. To eliminate spectral interference, a cepstrum based filtering method is proposed to separate various reflection features. In particular, the fundamental spectrum contributing to structural integrity can be extracted smoothly by removing harmonic fluctuations regarding wave reflections with an optimized filter. Subsequently, to establish the quantitative relationships between fundamental spectrum features and the impact energies, damage indices involving spectrum energy mean and median frequency shift are introduced to quantify the change of spectrum intensity and distribution respectively, which shows good performance on impact damage characterization. Finally, the experiment was carried out on a T300 composite beam, in which strong reflections come after direct waves. Meanwhile, the severity of impact damage was simulated by the free droppings of a steel ball with different heights. The results show the effectiveness of the proposed method for characterizing impact damages with improved sensitivity.

中文翻译：

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使用兰姆波对复合梁冲击损伤表征的改进谱方法

兰姆波谱方法是表征复合结构中不可见损伤的一种候选方法。不幸的是，几何边界引起的多次反射可能会扭曲兰姆波谱，这可能涵盖有关结构完整性的重要特征。为了消除光谱干扰，提出了一种基于倒谱的滤波方法来分离各种反射特征。特别是，通过使用优化的滤波器去除与波反射有关的谐波波动，可以平滑地提取有助于结构完整性的基本频谱。随后，为了建立基本光谱特征与冲击能量之间的定量关系，引入了包括频谱能量平均值和中值频移的损伤指数，分别量化了频谱强度和分布的变化，在冲击损伤表征方面表现出良好的性能。最后，实验是在 T300 复合光束上进行的，其中强反射在直接波之后出现。同时，通过不同高度钢球的自由落体模拟冲击损伤的严重程度。结果表明，所提出的方法在以提高的灵敏度表征冲击损伤方面是有效的。通过不同高度钢球的自由落体模拟冲击损伤的严重程度。结果表明，所提出的方法在以提高的灵敏度表征冲击损伤方面是有效的。通过不同高度钢球的自由落体模拟冲击损伤的严重程度。结果表明，所提出的方法在以提高的灵敏度表征冲击损伤方面是有效的。