In this study, both linear and nonlinear vibrational defect imaging is performed for a cross-ply carbon fiber-reinforced polymer (CFRP) plate with artificial delaminations and for a quasi-isotropic CFRP with delaminations at the edge. The measured broadband chirp vibrational response is decomposed into different components: the linear response and the nonlinear response in terms of the higher harmonics. This decomposition is performed using the short-time Fourier transformation combined with bandpass filtering in the time-frequency domain. The linear and nonlinear vibrational response of the defect is analyzed by calculation of the defect-to-background ratio. Damage maps are created using band power calculation, which does not require any user-input nor prior information about the inspected sample. It is shown that the damage map resulting from the linear band power shows high sensitivity to shallow defects, while the damage map associated to the nonlinear band power shows a high sensitivity to both shallow and deep defects. Finally, a baseline-free framework is proposed for the detection and localization of out-of-sight damage. The damage is localized by source localization of the observed nonlinear wave components in the wavenumber domain.

中文翻译：

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用于检测和定位复合材料中视内和视外缺陷的非线性弹性波能量成像

在这项研究中，对具有人工分层的交叉层碳纤维增强聚合物 (CFRP) 板和边缘分层的准各向同性 CFRP 进行了线性和非线性振动缺陷成像。测得的宽带啁啾振动响应被分解为不同的分量：线性响应和高次谐波的非线性响应。这种分解是使用短时傅立叶变换结合时频域中的带通滤波来执行的。通过计算缺陷与背景比来分析缺陷的线性和非线性振动响应。损伤图是使用带功率计算创建的，不需要任何用户输入，也不需要有关检查样品的先验信息。结果表明，由线性带功率产生的损伤图对浅缺陷表现出高灵敏度，而与非线性带功率相关的损伤图对浅缺陷和深缺陷均表现出高灵敏度。最后，提出了一种用于检测和定位视线外损坏的无基线框架。通过波数域中观察到的非线性波分量的源定位来定位损伤。