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首页> 外文期刊>Structural health monitoring >Imaging of local porosity/voids using a fully non-contact air-coupled transducer and laser Doppler vibrometer system
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Imaging of local porosity/voids using a fully non-contact air-coupled transducer and laser Doppler vibrometer system

机译：使用完全非接触式空气耦合换能器和激光多普勒振动计系统对局部孔隙/空隙成像

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摘要

This study exploits the feasibility of imaging zones of local porosity/voids simulated by introducing microspheres during layup of a unidirectional carbon fiber-reinforced polymer composite panel. A fully non-contact hybrid system primarily composed of an air-coupled transducer and a laser Doppler vibrometer was used for imaging the local porosity/void zones from the guided wave response. To improve image resolution, several preprocessing techniques are performed. The wavefield reconstructed from the laser Doppler vibrometer measurements was first denoised using a one-dimensional wavelet transform in the time domain followed by a two-dimensional wavelet transform in the spatial domain. From the total wavefield, the much weaker backscattered waves were separated from the stronger incident wave by frequency-wavenumber domain filtering. In order to further enhance the signal-to-noise ratio and sharpen the image, the attenuation of incident wave propagation to the damage site was compensated through two proposed weight functions. Finally, a zero-lag cross-correlation was performed for imaging the zone where the compensated incident and backscattered waves were in phase. This improved imaging condition, the denoised weighted zero-lag cross-correlation, was proposed and tested for defect imaging in the composite panel with eight intentionally introduced zones of high porosity/voids of varying diameters (1.59-6.35mm) and depths (0.36-1.08mm). As expected, the sensitivity of the non-contact air-coupled transducer/laser Doppler vibrometer hybrid system was limited by the wavelength of the excitation signal. The system incorporated with the denoised weighted zero-lag cross-correlation imaging condition for guided wave interrogation gave similar image quality in comparison with that by the immersion C-scan.
机译：这项研究利用了在单向碳纤维增强的聚合物复合板的铺放过程中引入微球体来模拟局部孔隙/空隙成像区域的可行性。主要由空气耦合换能器和激光多普勒振动计组成的完全非接触式混合系统用于根据导波响应对局部孔隙/空隙区域成像。为了提高图像分辨率，执行了几种预处理技术。首先使用时域中的一维小波变换对空域中的二维小波变换进行消噪，然后从激光多普勒测振仪的测量结果中重建出波场。通过频率-波数域滤波从总波场中将较弱的反向散射波与较强的入射波分离开。为了进一步提高信噪比并锐化图像，通过两个建议的权重函数补偿了入射波传播到损伤部位的衰减。最后，执行零延迟互相关以对补偿后的入射波和反向散射波同相的区域成像。提出并改善了这种成像条件，即去噪后的加权零滞后互相关，并针对复合面板中的缺陷成像进行了测试，该面板具有八个故意引入的高孔隙度/孔隙直径（1.59-6.35mm）和深度（0.36-0.36）的空隙。 1.08毫米）。不出所料，非接触式空气耦合传感器/激光多普勒振动计混合系统的灵敏度受到激发信号波长的限制。结合去噪加权零时滞互相关成像条件进行导波询问的系统与浸入式C扫描相比具有相似的图像质量。

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