For several years, CEA-LIST and partners have been developing ultrasonic simulation tools with the aim of modelling non-destructive evaluation. The existing ultrasonic modules allow us to simulate fully real ultrasonic inspection scenarios in a range of applications which requires the computation of the propagated beam, as well as its interaction with flaws. To fulfil requirements of an intensive use (for parametric studies), the choice has been made to adopt mainly analytical approximate or exact methods to model the scattering of ultrasound by flaws. The applied analytical theories (Kirchhoff and Born approximations, GTD, SOV...) were already described in previous GDR communication. Over the years, this "semi-analytical" approach has been enriched by adaptations and improvements of the existing models or by new models, in order to extend the applicability of the simulation tools. This paper is devoted to the following recent advances performed in the framework of this approach: The SOV method based on the exact analytical model for the scattering from a cylindrical cavity has been extended in 3D to account for field variations along the cylinder. This new 3D model leads to an improvement in simulation of small side-drilled holes. Concerning the geometrical theories of diffraction (GTD), subroutines for calculation of the 2D wedge diffraction coefficients (for bulk or Rayleigh incident waves) have been developed by the Waves and Fields Group and uniform corrections (UAT and UTD) are under investigation. Modelling of the contribution of the head wave and creeping wave to the echoes arising from a wedge. Numerous experimental validations of the developed models are provided. New possibilities offered by these new developments are emphasized.

https://iopscience.iop.org/article/10.1088/1742-6596/269/1/012013/pdf

Recent advances in semi-analytical scattering models for NDT simulation

This communication presents the results obtained on the configurations proposed in the 2009 UT modelling benchmark with the ultrasonic models implemented in the CIVA software platform. The aim, this year, is to study the relative amplitudes and the shapes of specular and corner echoes for different flaws in “2D” and “3D” configurations. Experiments have been performed with contact probes (single element or phased array) radiating transversal or longitudinal waves at 45° incidence angle on planar mock‐ups containing flat‐bottom hole, side‐drilled holes and backwall breaking notches of different heights and widths. The echoes are simulated by applying an integral formulation for the field radiated by the probe (the pencil‐model) and different scattering models depending on the kind of defects. Comparison between simulated and experimental results are presented and discussed.

Results of the 2009 ut modeling benchmark obtained with civa: responses of notches, side‐drilled holes and flat‐bottom holes of various sizes

This paper proposes a brief review of acoustic wave scattering models from rough surfaces. This review is intended to provide an up-to-date survey of the analytical approximate or semi-analytical methods that are encountered in acoustic scattering from random rough surfaces. Thus, this review focuses only on the scattering of acoustic waves and does not deal with the transmission through a rough interface of waves within a solid material. The main used approximations are classified here into two types: the two historical approximations (Kirchhoff approximation and the perturbation theory) and some sound propagation models more suitable for grazing observation angles on rough surfaces, such as the small slope approximation, the integral equation method and the parabolic equation. The use of the existing approximations in the scientific literature and their validity are highlighted. Rough surfaces with Gaussian height distribution are usually considered in the models hypotheses. Rather few comparisons between models and measurements have been found in the literature. Some new criteria have been recently determined for the validity of the Kirchhoff approximation, which is one of the most used models, owing to its implementation simplicity.

https://www.mdpi.com/2076-3417/10/22/8305/pdf

Acoustic Scattering Models from Rough Surfaces: A Brief Review and Recent Advances

The high frequency models gathered in the CIVA software allow fast computations and provide satisfactory quantitative predictions in a wide range of situations. However, the domain of validity of these models is limited since they do not accurately predict the ultrasound response in configurations involving subwavelength complex phenomena. In addition, when modelling backwall breaking defects inspection, an important challenge remains to capture the propagation of the creeping waves that are generated at the critical angle. Hybrid models combining numerical and asymptotic methods have already been shown to be an effective strategy to overcome these limitations in 2D [1]. However, 3D simulations remain a crucial issue for industrial applications because of the computational cost of the numerical solver. A dedicated three dimensional high order finite element model combined with a domain decomposition method has been recently proposed to tackle 3D limitations [2]. In this communication, we will focus on the specific case of planar backwall breaking defects, with an adapted coupling strategy in order to efficiently model the propagation of creeping waves. Numerical and experimental validations will be proposed on various configurations.

/pdf/ut-simulation-using-a-fully-automated-3d-hybrid-model-1n2vs5atvm.pdf

UT simulation using a fully automated 3D hybrid model: Application to planar backwall breaking defects inspection

The physical modeling and simulation of nondestructive evaluation (NDE) measurements has a major role in the advancement of NDE and structural health monitoring (SHM). In ultrasonic NDE (UNDE) simulations, evaluating the scattering of ultrasound by defects is a computationallyintensive process. Many UNDE system models treat the scattering process using exact analytical methods or high-frequency approximations such as the Kirchhoff approximation (KA) to make the simulation effort tractable. These methods naturally have a limited scope. This thesis aims to supplement the existing scattering models with fast and memory-efficient full-wave models that are based on the boundary element method (BEM). For computational efficiency, such full-wave models should be applied only to those problems wherein the existing approximation methods are not suitable. Therefore, the adequacy of different scattering models for representing various test scenarios has to be studied. Although analyzing scattering models by themselves is helpful, their true adequacy is revealed only when they are combined with models of other elements of the NDE system and the resulting predictions are evaluated against measurements. Very few comprehensive studies of this nature exist, particularly for full-wave scattering models. To fill this gap, two different scattering models– the KA and a boundary-element method– are integrated into a UNDE system model in this work, and their predictions for standard measurement outputs are compared with experimental data for various benchmark problems. This quantitative comparison serves as a guideline for selecting between the KA and full-wave scattering models for performing UNDE simulations. In accordance with theoretical expectations, the KA is shown to be inappropriate for modeling penetrable (inclusiontype) defects and non-specular scattering, such as diffraction from thin cracks above certain angles of incidence.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=9140&context=etd

Full-wave modeling of ultrasonic scattering for non-destructive evaluation

This paper aims at presenting an overview of the current capabilities of the ultrasonic models of the CIVA software platform (for ultrasonics, eddy current and radiography techniques), developed by CEA‐LIST and partners. Those models are based on semi‐analytical approaches and numerical integration (integral methods upon the surface of probe or the flaw) in order to address fairly complex configurations while keeping reduced computation times. Such skills are obviously reached within the range of validity of the semi‐analytical models, which have to be carefully studied. In this context, benchmarks organized by the World Federation of NDE Centers (WFNDEC) from 2004 have largely contributed, thanks to experimental data and comparison with other codes of the community, to the validation of simulation codes. Those benchmarks were mostly dealing with canonical problems (in terms of probes, component geometry and flaw shapes). This paper aims at summing up the various problems addressed in the benchmarks and their contribution to the extension of UT models in CIVA.

M. Darmon

Papers

An overview of ultrasonic beam propagation and flaw scattering models in the civa software