State Key Lab of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou 310027, China.
CRRC Zhuzhou Institute Co. Ltd., Zhuzhou 412001, China.
Sensors (Basel). 2019 Apr 6;19(7):1654. doi: 10.3390/s19071654.
A preliminary backscattered signal model of carbon-fiber-reinforced plastic (CFRP) laminate was established. The backscattered signal model was composed of three sub models, which were concerned with structural signal, scattering signal, and non-acoustic noise. Resonance in structural signal and echoes excited by defects (porosity and rich-resin) were studied. The results showed that: resonance would occur when there was sufficient bandwidth; when the CFRP laminate contained voids, the center frequency of the backscattered signal decreased; and the localized defects, including rich-resin and localized porosity, tended to generate apparent echoes where they located. A simplified backscattered signal model was subsequently put forward, showing certain potential in revealing time-frequency properties of backscattered signals. The newly proposed variational mode decomposition was used for defect modes extraction, successfully avoiding the mode mixing and false modes which easily exist in empirical mode decomposition. Subsequently, the generalized Stockwell transform was adopted for the defects localization. The simulation and experiment denoted the coincidence between the backscattered signal model and the experimental signal, and showed the effectiveness of variational mode decomposition and generalized Stockwell transform in localized defects detection.
建立了碳纤维增强塑料（CFRP）层压板的背散射信号初步模型。背散射信号模型由三个子模型组成，分别涉及结构信号、散射信号和非声噪声。研究了结构信号中的共振和缺陷（孔隙和富树脂）激发的回波。结果表明：当带宽足够时会发生共振；当 CFRP 层压板存在空洞时，背散射信号的中心频率降低；局部缺陷，包括富树脂和局部孔隙，往往会在其所在位置产生明显的回波。随后提出了简化的背散射信号模型，在揭示背散射信号的时频特性方面具有一定的潜力。新提出的变分模态分解用于缺陷模式提取，成功避免了经验模态分解中容易出现的模式混合和虚假模式。随后，广义斯托克斯变换用于缺陷定位。模拟和实验表明，背散射信号模型与实验信号之间存在一致性，并且表明变分模态分解和广义斯托克斯变换在局部缺陷检测中的有效性。
