A comparison and extensions of algorithms for quantitative imaging of laminar damage in plates. I. Point spread functions and near field imaging

Rose, L. R. F.; Chan, Eugene; Wang, Chun H.

doi:10.1016/j.wavemoti.2015.05.010

Cited by 30 publications

(45 citation statements)

References 61 publications

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“…The derivation of the relation relies on the far-eld approximation of the Green's function, which is suciently accurate when the distance between the imaging point and the point source is larger than 2λ. This approximation indicates that the damage should not be too close to the measurement array, which is generally satised in the context of SHM [18]. Figure 2.24 and 2.25 show reconstructed images for a centred and an o-centre circular scatterer using the MDT algorithm, respectively.…”

Section: Diraction Tomographymentioning

confidence: 85%

“…It means that, utilising the mode conversion eect, PWDT can be potentially developed as a baseline-free imaging method, which is attractive to NDE applications where baseline is not available or reliable. In addition, PWDT can be further extended to modied diraction tomography (MDT) to allow point source excitation and near-eld measurement [18], making it applicable to typical SHM systems, where individual piezoelectric transducer elements (PZT) are used to excite the interrogation waves [2,7,13].…”

Section: Background and Motivationmentioning

confidence: 99%

“…This is because for large damages, the required distance can become relatively large, leading to reduced SNR of the scattered eld. Recently, Rose et al [18] extended PWDT to image damage in the near-eld, leading to the modied diraction tomography (MDT) algorithm. This is achieved by deriving a relation between the scattering amplitude of the cylindrical wave from a point source and the plane-wave scattering amplitude introduced in PWDT [17,140].…”

Section: Diraction Tomographymentioning

confidence: 99%

“…As for the o-centre scatterer, the oset and the size of the scatterer are accurately reconstructed, but there is notable overshooting at the side near the measurement array, resulting in an over-estimation of the severity by about 15 %. However, it should be noted that although the MDT algorithm is developed for plate waves, in [18], the scattered eld for reconstructions are calculated using an analytical scattering model for acoustic waves. The performance of MDT is not clear when the actual plate wave scattered eld is used for imaging, which requires further investigations.…”

Section: Diraction Tomographymentioning

confidence: 99%

“…The performance of MDT is not clear when the actual plate wave scattered eld is used for imaging, which requires further investigations. Reconstruction results for a o-centre circular scatterer, using the modied diraction tomography algorithm developed in [18]. The scatterer is of radius a = λ and refractive index n = 1.05, and is centred at (8λ, 0).…”

Section: Diraction Tomographymentioning

confidence: 99%

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Applications of diffraction tomography on quantitative imaging using ultrasonic guided plate waves

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Critical infrastructures in transport and civil engineering applications can suer from structural damages such as fatigue cracks and corrosion due to extreme loading or environmental conditions. Under the commonly used damage tolerant design philosophy, structures will not fail if damages are limited in size and severity. However, if damages are not detected at the early stage and properly controlled, they may grow in terms of their sizes and severities, which can eventually lead to catastrophic failures. Therefore, it is important to monitor the onset and progression of structural damages to ensure the safety of critical infrastructure assets.Structural health monitoring (SHM) technologies have shown potential to improve the management of key structural components. Among the possible SHM techniques, guided wave testing using piezoelectric transducers as transmitter and receiver elements is an attractive methodology, because it enables fast scanning of large areas. To assess the structural integrity, a quantitative imaging method is required. One of the methods that has attracted major attention is guided wave or plate wave diraction tomography (PWDT) because it enables quantitative characterization of damages including location, size as well as severity. Although the performance of PWDT has been demonstrated to characterize, for example remaining plate thickness for corrosion damages, its reliability and versatility using dierent system congurations have not yet been systematically evaluated.This thesis aims to evaluate the performance of PWDT, and to understand the underlying physical mechanisms aecting its performance. It also investigates the feasibility of extending PWDT to other fundamental plate wave modes beyond the rst exural wave mode. Hence, the three major objectives of the thesis are: i) to quantitatively identify the applicable range of PWDT for reliable and accurate damage reconstructions for dierent wave modes; ii) to understand the physical mechanisms that aect the performance of PWDT reconstruction; and iii) to investigate the feasibility of developing a baseline-free imaging technique by considering mode conversion eects in the framework of PWDT.To achieve this comprehensive and fundamental understanding of PWDT and systematically evaluate its imaging quality, its performance to image circular blind hole damages in isotropic plates is evaluated. This requires the calculation of the scatter elds corresponding to the three fundamental plate wave modes using analytical models and including all possible mode conversion eects. In the case of incoming and scattered fundamental exural waves the damage characteristics, including size and severity are accurately estimated as long as the fundamental i limitations of the imaging algorithm are fullled, i.e. Born approximation and diraction limit.Hence the accuracy is generally lower for larger and deeper defects. For the fundamental symmetric Lamb wave mode, the imaging quality is superior for large and severe damages.However, the quality of the i...

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Section: Diraction Tomographymentioning

confidence: 85%