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

Abstract

The estimation of the size and location of defects in multi-layered composite structures by ultrasonic non-destructive testing using guided waves has attracted the attention of researchers for the last few decades. Although extensive signal processing techniques are available, there are only a few studies available based on image processing of the ultrasonic B-scan image to extract the size and location of defects via the process of ultrasonic non-destructive testing. This work presents an image processing technique for ultrasonic B-scan images to improve the estimation of the location and size of disbond-type defects in glass fiber-reinforced plastic materials with 25-mm and 51-mm diameters. The sample is a segment of a wind turbine blade with a variable thickness ranging from 3 to 24 mm. The experiment is performed by using a low-frequency ultrasonic system and a pair of contact-type piezoceramic transducers kept apart by a 50-mm distance and embedded on a moving mechanical panel. The B-scan image acquired by the ultrasonic pitch-catch technique is denoised by utilizing features of two-dimensional discrete wavelet transform. Thereafter, the normalized pixel densities are compared along the scanned distance on the region of interest of the image, and a −3 dB threshold is applied to the locations and sizes the defects in the spatial domain.

Fully Noncontact Hybrid NDT for 3D Defect Reconstruction Using SAFT Algorithm and 2D Apodization Window

“…Signal processing usually implemented through contact or noncontact ultrasonic techniques is based on the extraction of the time-of-flight (TOF) corresponding to the reflected echoes generated by the embedded defects. Several algorithms have been proposed, including the B-scan [12], Fourier-transform, short-time Fourier-transform (STFT) [13], wavelet transform (WT) [14,15], time reversal [16], and synthetic aperture focusing technique (SAFT) algorithms [12,17,18,19,20]. Each algorithm has advantages and limitations.…”

“…Superimposing the results of the three faces together is then performed to provide information about the defect from different angles/perspectives. We apply the three faces scanning and SAFT algorithm processing as a contribution to expand the one face scanning for SAFT analysis that is described in the literature [12,17,18,19,20,22,23]. In addition to the SAFT method, an enhanced 2D apodization function is implemented as a novel contribution that eliminates the side lobes generated by the exciter as an artifact in the input signal [24].…”

A Novel Image-Restoration Method Based on High-Order Total Variation Regularization Term

“…In the field of electronics and information, signal processing is a hot research topic, and as a special signal, the study of image has attracted the attention of scholars all over the world [1][2][3]. In image processing, image restoration is one of the most important issues and this issue has received extensive attention in the past few decades [4][5][6][7][8][9][10][11].…”

“…In the process of image deblurring under impulse noise, the main task is to find the unknown true image x ∈ R n 2 from the observed image f ∈ R n 2 defined by f = N imp (Kx) (1) where N imp denote the process of image degradation by impulse noise, and K ∈ R n 2 ×n 2 is a blurring operator. It is known that when K is unknown, the model deals with blind restoration, and when K is known, it deals with image denoising.…”

Fully Non-Contact Hybrid NDT Inspection for 3D Defect Reconstruction Using an Improved SAFT Algorithm

“…The signal processing usually implemented to contact or non-contact ultrasonic techniques is based on the extraction of the time of flight (TOF) corresponding to the reflected echoes generated by the embedded defects. Several algorithms are proposed in the literature, including the B-scan [7], Fourier transform, short time Fourier transform (STFT) [8], wavelet transform (WT) [9,10], time reversal [11] and synthetic aperture focusing technique (SAFT) algorithms [7,[12][13][14][15]. Each algorithm has advantages and limitations.…”