Modelling of scattering of ultrasounds by flaws for NDT

Darmon, Michel; Leymarie, Nicolas; Chatillon, Sylvain; Mahaut, S.

doi:10.1007/978-3-540-89105-5_6

Cited by 33 publications

(30 citation statements)

References 7 publications

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“…In this context hybrid modelling schemes display maximal advantage: a suitable scheme must be generic and independent of the constituent modelling techniques. Although hybrid modelling methods are commonly known in the literature and may be as old as the study of elastic wave scattering itself [20], most developments (including recent ones, such as [3] for efficient FE models and [48] where a CIVA-FE link is being pursued) are tied to specific sets of modelling techniques. We show how the limitation of the hybrid schemes to particular modelling techniques arises out of their fundamental formulation and give a formalism to generalize them.…”

Section: Discussionmentioning

confidence: 99%

A generic hybrid model for bulk elastodynamics, with application to ultrasonic nondestructive evaluation

Rajagopal

Skelton

Lowe

2012

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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Practical ultrasonic inspection requires modeling tools that enable rapid and accurate visualisation; due to the increasing sophistication of practical inspection it is becoming increasingly difficult to use a single modelling method to represent an entire inspection process. Hybrid models that utilize different or interacting numerical schemes in different regions, to use their relative advantages to maximal effect, are attractive in this context, but are usually custommade for bespoke applications or sets of modelling methods. The limitation of hybrid schemes to particular modelling techniques is shown here to be related to their fundamental formulation. As a result it becomes clear that a formalism to generalize hybrid schemes can be developed: an example of how such a generic hybrid modelling interface is constructed is illustrated for the abstraction of bulk ultrasonic wave phenomena, common in practical inspection problems. This interface is then adapted to work within a prototype hybrid model consisting of two smaller Finite Element model-domains, and explicitly demonstrated for bulk ultrasonic wave propagation and scattering examples.Sources of error and ways of improving the accuracy of the interface are also discussed.

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Section: Discussionmentioning

confidence: 99%

A generic hybrid model for bulk elastodynamics, with application to ultrasonic nondestructive evaluation

Rajagopal

Skelton

Lowe

2012

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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“…In combination with the long sound paths in the present problem, volume discretization-based methods, such as finite element method (FEM) and finite difference time domain (FDTD), are thus deemed suboptimal [22]. Here, an elastodynamic simulation in the Kirchhoff approximation is used [23], which, while it does not model all elastodynamic wave phenomena, is nonetheless frequently applied in NDT [24]. Based on the high-frequency asymptotics, it is expected to become inaccurate for small defects.…”

Section: Numerical Simulationmentioning

confidence: 98%

Ultrasonic Defect Characterization in Heavy Rotor Forgings by Means of the Synthetic Aperture Focusing Technique and Optimization Methods

Fendt

Mooshofer

Rupitsch

et al. 2016

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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Ultrasonic nondestructive testing of steel forgings aims at the detection and classification of material inhomogeneities to ensure the components fitness for use. Due to the high price and safety critical nature of large forgings for turbomachinery, there is great interest in the application of imaging algorithms to inspection data. However, small flaw indications that cannot be sufficiently resolved have to be characterized using amplitude-based quantification. One such method is the distance gain size method, which converts the maximum echo amplitudes into the diameters of penny-shaped equivalent size reflectors. The approach presented in this contribution combines the synthetic aperture focusing technique (SAFT) with an iterative inversion scheme to locate and quantify small flaws in a more reliable way. Ultrasonic inspection data obtained in a pulse-echo configuration are reconstructed by means of an Synthetic Focusing Technique (SAFT). From the reconstructed data, the amount and approximate location of small flaws are extracted. These predetermined positions, along with the constrained defect model of a penny-shaped crack, provide the initial parametrization for an elastodynamic simulation based on the Kirchhoff approximation. The identification of the optimal parameter set is achieved through an iteratively regularized Gauss-Newton method. By testing the characterization method on a series of flat-bottom holes under laboratory conditions, we demonstrate that the procedure is applicable over a wide range of defect sizes. To show suitability for large forging inspection, we additionally evaluate the inspection data of a large generator shaft forging of 0.6-m diameter.

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“…In practice, its evaluation generally requires various degrees of approximation, depending on the approach. In many approaches the expression is approximated in ways that allows replacing the integrand by plane-wave interaction coefficients [1][2][3]. These coefficients have been obtained analytically for several approximations and types of flaws.…”

Section: = (mentioning

confidence: 99%

“…Plane-wave scattering coefficients are used by many semi-analytical methods, including those described by Thompson and Gray [1] and by Schmerr and Song [2], as well as those implemented in the Civa software [3]. Planewave and quasi plane-wave approximations of the ultrasonic fields provide the input values for the calculations of these coefficients.…”

Section: Introductionmentioning

confidence: 99%

Improved semi-analytical simulation of UT inspections using a ray-based decomposition of the incident fields

Dorval¹,

Leymarie²,

Chatillon³

2016

AIP Conference Proceedings

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Abstract. Semi-analytical models are often used for computationally efficient ultrasonic simulations. They typically apply plane-wave or quasi plane-wave approximations to the ultrasonic fields at the location of flaws in order to calculate diffraction coefficients. In favorable cases, the plane-wave approximations used for echo computations in the Civa software yield satisfying results. However, it can lead to inaccuracies in unfavorable cases, such as for wide probe apertures, outside of the focal region, or for beam-splitting or distortion due to irregular geometries. This communication presents an improved model, implemented in a development version of the software. The new approach describes the ultrasonic field as a sum of rays and applies the plane-wave approximation to each ray instead of the entire field. It significantly improves the accuracy of echo computations. However, it implies that the diffraction is calculated for each pair of incident and diffracted rays instead of being calculated only once: a specific algorithm has been developed in order to avoid a significant increase in computation times. Benefits of the new approach are illustrated by comparing its results and computation times to those of the former plane-wave model in several cases of interest. They are also compared to those of a coupled finite element model (Civa-Athena).

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Modelling of scattering of ultrasounds by flaws for NDT

Cited by 33 publications

References 7 publications

A generic hybrid model for bulk elastodynamics, with application to ultrasonic nondestructive evaluation

A generic hybrid model for bulk elastodynamics, with application to ultrasonic nondestructive evaluation

Ultrasonic Defect Characterization in Heavy Rotor Forgings by Means of the Synthetic Aperture Focusing Technique and Optimization Methods

Improved semi-analytical simulation of UT inspections using a ray-based decomposition of the incident fields

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