P. Lanceleur

Acoustic properties of wood in tridimensional representation of slowness surfaces.

Mechanical behaviour of wood considered as an orthotropic solid can be determined with ultrasonic technique. The propagation phenomena in wood are complex and theoretically are regulated by Christoffels equation. Three type of waves can propagate in wood. During the propagation phenomena three slowness sheets are observed, corresponding to a fast longitudinal wave (inner sheet) and two shear waves, one fast and one slow (outer sheet). These waves are submitted continuously to mode conversion phenomena. The polarization angle changes when the propagation direction is out of the principal directions of symmetry of the material. In this article an analysis of the propagation phenomena in tridimensional representation is performed for different wood species. This approach contributes to the understanding of dynamic aspects of particle displacement associated with the wave fronts propagation. Globally, the anisotropy of each species, expressed by their acoustical behaviour is well represented.

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>>

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.

Frequency-dependant homogenized properties of composite using spectral analysis method

An inverse procedure is proposed to determine the material constants of multilayered composites using a spectral analysis homogenization method. Recursive process gives interfacial displacement perpendicular to layers in term of deepness. A fast-Fourier transform (FFT) procedure has been used in order to extract the wave numbers propagating in the multilayer. The upper frequency bound of this homogenization domain is estimated. Inside the homogenization domain, we discover a maximum of three planes waves susceptible to propagate in the medium. A consistent algorithm is adopted to develop an inverse procedure for the determination of the materials constants of multidirectional composite. The extracted wave numbers are used as the inputs for the procedure. The outputs are the elastic constants of multidirectional composite. Using this method, the frequency dependent effective elastic constants are obtained and example for [0/90] composites is given.

Modeling of inhomogeneous monochromatic plane wave at the interface between two arbitrary homogeneous anisotropic absorbent media

This work aims to model the interaction of an inhomogeneous monochromatic oblique plane wave with a plane interface separating two semi‐infinite homogeneous media. These media can be either isotropic or anisotropic, absorbent or not. A numerical method is proposed to generalize previously developed procedures, which were restricted to the case of incident homogeneous waves, interacting with absorbing materials. In this case the waves propagating are always inhomogeneous. Due to this inhomogeneity of the waves, the choice of compatible parameter for the incident wave is to be done on an energy criterion and not necessarily on a radiation one. The computation of all the parameters of all the involved waves makes several unexpected phenomena or behaviors to arise. For instance, by applying the study to the case of a water/nickel monocrystal interface, incident directions for which the energy flow vector is directed toward the transmission medium, whereas the slowness vector is directed toward the incident me...

Influence of attenuation on the behavior of refracted elastic waves at the interface between anisotropic media

During the ultrasonic non-destructive evaluation of complex materials, like multilayer or composite materials, the behavior of the ultrasonic waves at the interface of samples is strongly dependent upon the anisotropy as well as the attenuation characteristics of the propagation media. In the generally arbitrary case, the incident wave is assumed to be inhomogeneous. Therefore the application of the Snell-Descartes laws requires to consider the real as well as the imaginary parts of all the quantities encountered during the study. In that aim, we use a representation of the complex slowness curves so-called slowness interface curves which point out the evolution of the interaction of the waves at the interface with the inhomogeneity factors, i.e. the imaginary part of the slowness vectors. The continuous distortion of the curves with the inhomogeneity factor increasing is an interesting approach of these complicated phenomena.

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

INDICATION OF THE PHENOMENON OF ULTRASOUND DISPERSION IN COMPOSITES BY A TIME FREQUENCY REPRESENTATION

Time frequency representation methods are well adapted to the study of time varying signals and dispersion phenomena. A time frequency analysis is presented for the echographic signal obtained on a concentrated porosity and for the transmitted signal obtained at oblique incidence through a defect free composite.

DETERMINATION OF TRANSIENT DEFORMATIONS ON THE ACTIVE SURFACE OF N.D.E. ULTRASONIC ELEMENTS

A method based on a finite element analysis is presented which permits the calculation and the visualization of deformations of ultrasonic transducers in different configurations. 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 developped at Universite de Technologie de Compiegne (UTC) for the monochromatic case. The work reported in this paper deals with the adaptation and validation of the method for the multi-frequency excitation case, which is a more realistic approach used in the field of ultrasonic NDE.

Visualization of transient behaviour of piezoelectric ceramics by means of finite elements method

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. These methods were originally developed in the monochromatic case: one of the difficulties of this work was the adaptation and the validation of the methods in the multifrequency excitation cases, more realistic in the area of nondestructive examination (NDE) using ultrasonic methods. Several geometries were then tested, and an experimental confirmation of the results was achieved.<<ETX>>