Identification and Characterization of Defects in Glass Fiber Reinforced Plastic by Refining the Guided Lamb Waves

Abstract

In this paper, the disbond-type defect presented on glass fiber reinforced plastic material is analyzed by refining the guided Lamb wave signals. A segment of wind turbine blade is considered as a test sample. The low-frequency ultrasonic measurement system is used for the non-destructive testing of the test sample using guided waves. The P-1 type macro-fiber composite transducer as a transmitter and contact-type piezoceramic transducer as a receiver are used for the testing of a sample. The disbond type defect having a diameter of 81 mm is detected from the experimental results. To improve the accuracy in locating and sizing the defects and estimation of the time of flight and phase velocity of ultrasonic guided waves in defective region, signal processing algorithm is developed by utilizing the promising properties of various ultrasonic signal processing techniques such as wavelet transform, amplitude detection, two-dimensional Fast-Fourier transform, Hilbert transform and variational mode decomposition. The discrete wavelet transform is used to denoise the guided wave signals and then, the size and location of defects are estimated by amplitude detection. The reflected wave signals from the opposite edge of the sample are removed by applying the two-dimensional Fast-Fourier transform to the experimental B-scan signal. Afterwards, variational mode decomposition and Hilbert transform are used for the phase velocity and time-delay estimation by comparing the instantaneous amplitudes of the defective and defect-free signal. The validation and the demonstration of reproducibility of the algorithm is performed by extracting the features of a 51 mm defect from another experimental B-scan.

Defect Estimation in Non-Destructive Testing of Composites by Ultrasonic Guided Waves and Image Processing

“…Either a signal processing or image processing approach can be applied to improve the accuracy in the measurement. Many signal processing techniques have been used for the refinement of experimental results by analyzing the amplitudes, phase velocity, instantaneous frequencies, or time of flight of the received signals [4,[28][29][30][31][32]. However, the consideration of the experimental results as an image requires an effective image processing technique to extract the defect features.…”

“…There are many transformation techniques available for denoising an image, including Wiener filter processing, median filter, mode decomposing techniques such as EMD and VMD, etc. However, DWT has certain advantages as compared with short-time Fourier transform (STFT) and mode decomposition techniques in terms of variable window size [32,37]. Moreover, DWT provides temporal information in addition to amplitude and frequency information, which is lost in other transformations [38].…”

“…All the components, including the transducers and the LF ultrasonic system, was developed at the Ultrasound Research Institute of Kaunas University of Technology. The characteristics of the LF ultrasonic system are presented in Table 1 [31,32,37]. Before inspecting the sample for the analysis of defects, a linear scanning in the defect-free region was performed to estimate the dispersion curve.…”

“…A photo view of the experiment is presented in Figure 2a, and the acquired B-scan is shown in Figure 2b. In the ultrasonic NDT, two-dimensional fast Fourier Transform (2D-FFT) is used to transform the B-scan (time-distance measurements) into the phase the velocity-frequency domain [30,32,50]. The basic principle of 2D-FFT is the representation of GW propagation by the transfer function (H) of arrival time and scanning distance.…”

Eddy Current Array Inspection of Damaged CFRP Sandwich Panels

“…Ultrasonic inspection of sandwich panels is common (e.g., Refs. [10][11][12][13][14][15][16][17][18]), and a very basic American Society for Testing and Materials (ASTM) standard practice guide (ASTM E2580) for inspection of flat panels has been developed. Guided wave inspection appears to be particularly suitable for detecting disbonds in BVID, partly because of its ability to inspect large areas at once.…”