Hugues Duflo - Academia.edu (original) (raw)

Papers by Hugues Duflo

Ultrasonics, 2004

This paper deals with a quantitative study of the conversion of a Lamb wave at the bevelled edge ... more This paper deals with a quantitative study of the conversion of a Lamb wave at the bevelled edge of a plate. A harmonic wave (successively the A1 and S0 Lamb modes) is generated using a wedge. The normal displacements at the surface of the plate are measured with a laser vibrometer and used to compute an energy evaluation. In order to determine a good mean value of incident and reflected wave amplitudes, the signals are isolated by a Fourier treatment. Then, the energy flow repartition among the converted modes is computed in both cases and for different values of the bevel angle.

The Journal of the Acoustical Society of America, 2003

This study concentrates on the reflection of Lamb waves at the free end of a plate. The conversio... more This study concentrates on the reflection of Lamb waves at the free end of a plate. The conversion phenomena are examined in detail over a large frequency range and the energy conversion coefficients are obtained by three different ways: theoretically, numerically (finite element method) and experimentally. The experimental energy determination is obtained from the measurement of the plate normal displacements, by mean of a laser interferometer. All results are in relatively good agreement and the energy balance between incident and reflected waves is discussed in each case.

The Journal of the Acoustical Society of America, 2005

This paper deals with the reflection of a two-dimensional harmonic Lamb wave at the beveled end o... more This paper deals with the reflection of a two-dimensional harmonic Lamb wave at the beveled end of a plate. The existence of a resonant edge mode is described by a numerical model. It is proved that the edge mode is the resonance of different complex modes. The behavior of this mode as a function of the bevel angle is studied. Its amplitude decreases and its resonance frequency shifts as the bevel angle decreases from 90 to 85 deg. An unexpected strong variation of the repartition of the reflected energy is linked to this phenomenon.

ABSTRACT We present a theoretical two-dimensional study of mode conversions that occur when an ha... more ABSTRACT We present a theoretical two-dimensional study of mode conversions that occur when an harmonic incident wave is reflected at the bevelled edge of a steel plate. A Lamb wave (A1, A0 or S 0 modes) is excited in a steel plate for different values of the frequency-thickness product. The energies of the reflected modes (A1, A0, S0, S1 or S2 mode) are computed in order to know the reflected coefficients. Several results are presented for various bevel angles. These results are confirmed by a finite element computation.

Acoustics letters, 2000

This work is a quantitative study of the interaction of Lamb waves with a welded rib. The experim... more This work is a quantitative study of the interaction of Lamb waves with a welded rib. The experimental energy determination is obtained from measurements of the plate normal displacements using a laser interferometer. At the plate-rib joint, the energy flow repartition among the converted waves is evaluated. Comparison of the experimental results with a finite element simulation shows the influence of the weld fillet shape on the wave transmission to the rib.

$Research paper thumbnail of Scholte wave diffraction by a dihedral: Study at oblique incidence$

The Journal of the Acoustical Society of America, 1995

ABSTRACT The geometrical theory of diffraction established by Keller allows one to describe the i... more ABSTRACT The geometrical theory of diffraction established by Keller allows one to describe the interaction between a bulk wave and a dihedral edge. It is experimentally verified that Keller's laws are also valid to describe the interaction of a sur;face wave (the Scholte-Stoneley wave) with the edge of an elastic dihedral. The diffracted energy is on Keller's cone. (C) 1995 Acoustical Society of America.

$Research paper thumbnail of Diffraction de l'onde de scholte. Diedre sous incidence oblique. Etude de reseaux de stries$

Journal of the Acoustical Society of America, 2016

The Journal of the Acoustical Society of America, 2008

The excellent and specific properties of composite materials in the various fields such as aerona... more The excellent and specific properties of composite materials in the various fields such as aeronautics, transport, energy, the nuclear power and civil engineering led to the need of knowing their behaviours in presence of defect (crack, ageing, delamination...). Therefore, the aim of this paper is to study the thermal ageing of the carbon fibre reinforced composite plates, using their nonlinear behaviours. The method used to achieve this work is the NEWS method (Non-linear Elastic Wave Spectroscopy), where some alternatives of this one are used. SIMONRUS which involves a study of the nonlinear response of a single resonant mode of the plate according to various amplitudes of excitation. In this case, the nonlinear phenomena analysed are resonance frequency shift and damping characteristic of different level ageing of plate. Evolution of non linear effects are then correled to ageing duration.

ABSTRACT The fabrication of composite materials from a fibrous matrix provides excellent mechanic... more ABSTRACT The fabrication of composite materials from a fibrous matrix provides excellent mechanical properties. However, the manufacturing processes involved is questioning on the minimization of related defects due to trapped gas bubbles during the impregnation. Indeed, the resin flow along the fibers, even under pressure, can result in residual porosity i.e. sources of defects on the finished product. In particular, the detection of bubbles is implemented for the development of composite materials by a Resin Transfer Molding (RTM) process. For this, we propose a method of ultrasonic detection, using a phased array transducer.

Dans le cadre d'une étude portant sur le suivi de polymérisation de matériau composite, une étude... more Dans le cadre d'une étude portant sur le suivi de polymérisation de matériau composite, une étude est réalisée sur des huiles de viscosité calibrée. La viscosité des fluides est liée aux phénomènes dissipatifs décrits en mécanique des fluides. Elle est mesurable notamment par une sollicitation périodique en cisaillement (fréquence de l'ordre du Hz). Ces phénomènes dissipatifs peuvent se mesurer au moyen d'ondes ultrasonores (fréquence de l'ordre du MHz). Pour cela, un dispositif expérimental approprié aux futures conditions de mesure est proposé. Le fluide étudié est placé entre 4 cm de verre et une plaque épaisse d'aluminium. L'épaisseur du fluide est de l'ordre de 6 mm. Les incertitudes liées aux conditions expérimentales sont quantifiées et leur incidence sur la précision de la mesure est discutée. Les résultats des deux mesures, mécanique et ultrasonore, sont confrontés et une corrélation est établie entre les résultats de trois huiles de viscosité calibrée. Ces données sont alors utilisées afin de déterminer la viscosité d'un fluide par la méthode ultrasonore.

Dans le but de tester localement une structure dans les industries de l'aéronautique, on a souven... more Dans le but de tester localement une structure dans les industries de l'aéronautique, on a souvent recours à des moyens d'évaluation non destructive (END). La mesure d'impédance électromécanique figure parmi les techniques permettant de caractériser les matériaux. En mettant un transducteur piézoélectrique ultrasonore en contact direct avec la plaque à tester, avec un film de gel de couplage pour assurer une bonne transmission des ondes ultrasonores, on vient modifier la résonance du transducteur. En appliquant une tension entre les deux électrodes du transducteur, on relève un courant électrique caractéristique de l'impédance de l'ensemble transducteur couplé à une plaque.

Acta Acustica united with Acustica

We present a two-dimensional study of mode conversions that occur when a harmonic incident wave i... more We present a two-dimensional study of mode conversions that occur when a harmonic incident wave is reflected at the bevelled edge of a steel plate. A harmonic Lamb wave (A0, A1, or S0 mode) is excited in a steel plate for different values of the frequency-thickness product. Firstly, a theoretical method is performed to compute the energies of the reflected modes (A0, A1, S0, S1 and S2 mode) in order to obtain the reflection coefficients. Several results are obtained for various bevel angles. They are successfully confirmed by a finite element computation and finally by measurements obtained with a laser interferometer.

An experimental setup has been developed for the monitoring of ultrasonic parameters during polym... more An experimental setup has been developed for the monitoring of ultrasonic parameters during polymerization in the context of the monitoring of composite plate production. An analytical approach is proposed based on the modeling of the wave velocity fitted by a Weibull distribution and was investigated to validate this approach by the Debye series modeling (DSM).The monitoring of the cured epoxy is also performed after curing in order to study the thermal transformation compared with DSC measurements. As a result, an approximated frequency-temperature (f, T) model is proposed for attenuation and velocity frequency and temperature dispersions.

La caractérisation expérimentale ultrasonore des propriétés viscoélastiques des matériaux fait ap... more La caractérisation expérimentale ultrasonore des propriétés viscoélastiques des matériaux fait apparaitre une dispersion relative importante. La reproductibilité de l'incidence normale et la sensibilité thermique des propriétés ont été identifiés comme des paramètres prépondérants. Leur impact est étudié dans la perspective d'une application sur un suivi de fabrication de plaques composites par le procédé RTM. Afin d'évaluer la sensibilité de la caractérisation à ces phénomènes perturbateurs, les paramètres ultrasonores que constituent l'atténuation et la vitesse de phase ont été mesurés à température ambiante pour deux références d'huiles silicones 47V50 et 47V350 (Rhodorsil ®). Plusieurs méthodes et variantes de caractérisation ont été mises en oeuvre : temps de vol, inter-corrélation et méthode spectrale. Ainsi, les paramètres ultrasonores sont présentés après avoir été corrigés en lien avec la sensibilité des mesures à la température ambiante. La dispersion e...

Ultrasonics, 2015

Defects may appear in composite structures during their life cycle. A 10MHz 128 elements phased a... more Defects may appear in composite structures during their life cycle. A 10MHz 128 elements phased array transducer was investigated to characterize join bonds and defects in sandwich honeycomb composite structures. An adequate focal law throughout the composite skin gives the ultrasonic dispersive properties of the composite skin and glue layer behind. The resulting B-scan cartographies allow characterizing locally the honeycomb adhesion. Experimental measurements are compared in good agreement with the Debye Series Method (DSM). In the processed C-scan image, flaws are detectable and measurable, localized both in the scanning plane and in the thickness of the composite skin.

2006 IEEE Ultrasonics Symposium, 2006

ABSTRACT

2007 IEEE Ultrasonics Symposium Proceedings, 2007

This study relates to the thermo-oxidative ageing of plates up to 5000 hours (at 160 or 180degC).... more This study relates to the thermo-oxidative ageing of plates up to 5000 hours (at 160 or 180degC). The electro-mechanical impedance of a commercial transducer (2.25 MHz or higher) coupled to the composite plate is measured. We give here a method to determine the speed and the attenuation of longitudinal waves, propagating along the thickness direction, using an inverse procedure on the impedance of the composite plate. The transducer is modelled and the parameters of this model are identified. The system of the transducer coupled with the composite plate is then studied. We show that the acoustic impedance of the propagation medium can be extracted provided the transducer's parameters are known. This method, applied to composite plates aged thermically, shows modifications of the parameters (velocity and attenuation). These variations are in good agreement with those obtained by other techniques carried out in laboratory which are also reliable but less practice to use "under wings".