Time-of-flight diffraction (TOFD) technique for accurate sizing of surface-breaking cracks

Baby, Sony; Balasubramanian, T.; Pardikar, R. J.; Palaniappan, M.; Subbaratnam, R.

doi:10.1784/insi.45.6.426.52885

Cited by 50 publications

(19 citation statements)

References 3 publications

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“…For cracks whose tip is close to the inspection surface, there might be significant overlap of the tip-diffracted signal and the lateral wave which travels between the transducers along the surface, as observed by Baby et al [6]. The accuracy of the crack measurement depends on the ability to determine the arrival times accurately, which in turn depends on the resolution of the timing measurement system.…”

Section: Overview Of Ultrasonic Methodsmentioning

confidence: 98%

Accurate depth measurement of small surface-breaking cracks using an ultrasonic array post-processing technique

Felice

Velichko

Wilcox

2014

NDT & E International

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a b s t r a c tIn this paper, the half-skip configuration of the Total Focusing Method (TFM) is used to image and size surface-breaking cracks. The TFM is an ultrasonic array post-processing technique which is used to synthetically focus at every image point in a target region. This paper considers the case of inspecting for cracks which have initiated from the far surface of a parallel-sided sample using an array on the near surface. Typically, only direct ray paths between the array and image points are included in the TFM algorithm and therefore the image obtained for this case consists only of root and tip indications; no specular reflection from the crack faces is captured. The tip indication often has such a poor signal-to-noise ratio that reliable crack depth measurement is challenging. With the Half-Skip TFM, instead of using directly-scattered signals, the image is formed using ultrasonic ray paths corresponding to the ultrasound that has reflected off the back surface and has then undergone specular reflection from the crack face back to the array. The technique is applied to experimental and simulated array data and is shown to measure the depth of small cracks (depth o1 mm) with greater reliability than methods which rely on tip diffraction.

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Section: Overview Of Ultrasonic Methodsmentioning

confidence: 98%

Accurate depth measurement of small surface-breaking cracks using an ultrasonic array post-processing technique

Felice

Velichko

Wilcox

2014

NDT & E International

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“…TOFD inspection has the property of high accuracy, high reliability, and especially the adequate location of the defect [2]. Ultrasonic TOFD technique uses the diffraction echo to determine the defects quantitatively.…”

Section: Introductionmentioning

confidence: 99%

Multiframe Ultrasonic TOFD Weld Inspection Imaging Based on Wavelet Transform and Image Registration

et al. 2018

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TOFD (time of flight diffraction) is a kind of weld defect detection technology by using ultrasonic diffraction wave signal. Because the diffraction intensity is far less than ultrasonic echo wave intensity, thus, the noise contained in TOFD signal is fairly large, and the formed image is not clear enough. Therefore, it is difficult to determine the size of defects accurately. In this paper, a method of noise reduction of TOFD signal and improving the resolution of the image are discussed based on the combination of wavelet thresholding and image registration. Wavelet multiresolution analysis method is adopted and the A-scan signal is decomposed into different frequency components. We propose a new threshold function to process the wavelet coefficients, which guarantees to denoise while preserving the useful information as much as possible. Setting up the ultrasonic TOFD inspection system and the image data with randomly distributed noise can be obtained via fine shake of the probes during testing. Then, image registration based on maximum correlation and blending is adopted to eliminate the noise in further step. The result shows that the proposed method can achieve denoising, together with resolution enhancement.

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“…Date 8 employed the surface wave transmission method to measure the crack depth to a scale as small as 0.82 mm with a mean error of 0.01 mm using a 5 MHz probe. Similarly, Baby 11 employed time-of-flight diffraction to estimate crack depth in the range of 1.68-19.04 mm with excellent accuracy by using 4 MHz angle beam probes. However, time-domain methods are not appropriate for the evaluation of a surface crack with a depth less than 0.8λ, due to the irregular time delay effect.…”

Section: Introductionmentioning

confidence: 99%

Estimation of Surface Crack Depth using Rayleigh Waves by Electromagnetic Acoustic Transducers

He¹,

Deng²,

Lu³

et al. 2017

IJAV

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A quantitative characterization method is introduced for estimating surface crack depth using Rayleigh waves in pitch-catch mode by electromagnetic acoustic transducers (EMATs). The method employs the experimentally determined reflection and transmission coefficients of Rayleigh waves scattered at a surface crack, which will be compared to the reference curves obtained from two-dimensional finite element method (FEM) simulations based on variable crack depth. Three EMAT couples with different centre frequencies were employed to extend the measuring range, and to implement the quantitative characterization of crack depth. The reference curves and measurement results were verified to be repeatable with great accuracy, which shows a maximum error of 17% with crack depth ranging from 0.2-3.0 mm.

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Time-of-flight diffraction (TOFD) technique for accurate sizing of surface-breaking cracks

Cited by 50 publications

References 3 publications

Accurate depth measurement of small surface-breaking cracks using an ultrasonic array post-processing technique

Accurate depth measurement of small surface-breaking cracks using an ultrasonic array post-processing technique

Multiframe Ultrasonic TOFD Weld Inspection Imaging Based on Wavelet Transform and Image Registration

Estimation of Surface Crack Depth using Rayleigh Waves by Electromagnetic Acoustic Transducers

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