J.F. de Belleval

Importance of the near Lamb mode imaging of multilayered composite plates

In recent years Lamb waves are being used for internal defect detection in multilayered composite plates. Different Lamb modes generate various stress levels in different layers. As a result, all Lamb modes are not equally sensitive to internal defects of various layers. A number of studies have been carried out to identify which Lamb mode is most effective for detecting defects in a specific layer. However, one shortcoming of the Lamb wave inspection technique is that in a symmetrically layered composite plate stress and displacement magnitudes and energy distribution profiles for all Lamb modes are symmetric about the central plane of the plate. As a result, the ability of a Lamb mode to detect defects in a specific layer of the plate is identical to its ability to detect defects in the corresponding layer of mirror symmetry. Hence, from the Lamb wave generated image one cannot distinguish between the defects in these two layers of mirror symmetry. In this paper it is investigated how by fine-tuning the frequency and the striking angle of the incident beam in the neighborhood of a Lamb mode one can separately detect internal defects in layers of mirror symmetry in the upper and lower halves of a plate.

Modelling of the ultrasonic field by the angular spectrum method in presence of interface.

We present a numerical modelling of the harmonic sound in two isotropic media, one liquid and the other solid separated by a plane interface. This numerical modelling is carried out by the angular spectrum method. This latter is applied to calculate the displacement potential generated by a rectangular transducer with a Gaussian profile and with an uniform profile. The rigorous modelling of the field needed to find the optimal parameters of the decomposition according to the transducer aperture and the ultrasonic wave frequency.

Deviation of a monochromatic Lamb wave beam in anisotropic multilayered media: asymptotic analysis, numerical and experimental results

The aim of this paper is threefold: to describe the physical phenomenon of the excitation of modal waves such as Lamb waves, in anisotropic multilayered media, by a monochromatic incident beam, using an asymptotic approach; to present a three-dimensional model using the decomposition of the incident beam into monochromatic plane waves (the formalism is applied to the particle displacement vector); to illustrate the phenomenon both numerically and experimentally. Numerical and experimental maps of the reflected field of pressure are presented, and the reradiation of the Lamb wave beam in an oblique plane is theoretically and numerically illustrated.

Modeling of transient deformation of piezoelectric ceramics (US NDE)

A method based on a finite-element analysis that permits the calculation and the visualization of deformations of ultrasonic transducers, in different configurations is presented. The method uses a Fourier series synthesis giving deformation of the free surface and electrical admittance for wide frequency bands by the use of finite-element procedures previously developed at Universite de Technologie de Compiegne (UTC). The method was originally developed for the monochromatic case. The authors report on the adaptation and validation of the method for the multifrequency excitation case, which is a more realistic approach used in the field of ultrasonic NDE. Several geometries were tested. In spite of the limitations of the method, due to the calculation requirements, the results show the role of the radial displacement behavior usually neglected in monodimensional analysis.<<ETX>>

Modeling of Ultrasonic Beam Interaction with an Anisotropic Multilayered Medium, Using Angular Spectrum Method

In many domains of acoustic field propagation, such as ultrasonic non-destmctive testing, a realistic calculation of ultrasonic beam patterns requires treatment of the effects of refraction and reflection from finite and infinite media. Application of the Angular Spectrum Analysis (ASA) to calculate the acoustic fields has become an increasingly interesting topic, because the ASA is easy to be numerically implemented upon the basis of the Fast Fourier Transform and can be used effectively to solve a variety of complex problems, especially those involved with boundaries and multilayered anisotropic media.

Characterization of flaws using the poles and zeros of the transfer function of the corresponding ultrasonic system

Abstract This investigation deals with a technique of flaw characterization which exploits the spectral phase of the echographic signal as a principal parameter. A method has been developed to determine the distribution of the poles and zeros of the transfer function of the echographic system in the complex plane. It seems to be easier to exploit this distribution rather than dealing directly with the spectral amplitude and phase. The results obtained on several artificial flaws are presented.

Dispersion Curves Analysis for Bonded Plates at Low Fd

Today the use of adhesive bonds is more developed in many industries and more specifically in Space Industries. Its development is limited by the possibility to make a non-destructive evaluation of the quality of the bond. Up to now, the inspection of the cohesion and the thickness of the glue are well controlled. With regard to the adhesion, the problem is not yet solved.

EXISTENCE DE DOMAINES ANGULAIRES DISJOINTS DE GÉNÉRATION DES ONDES RÉFRACTÉES DANS UN MATÉRIAU ANISOTROPE : NOUVELLE NOTION D'ANGLE CRITIQUE

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. EXISTENCE DE DOMAINES ANGULAIRES DISJOINTS DE GÉNÉRATION DES ONDES RÉFRACTÉES DANS UN MATÉRIAU ANISOTROPE : NOUVELLE NOTION D’ANGLE CRITIQUE H. Ribeiro, J. De Belleval, P. Lanceleur