Acoustic Wood anomalies are phenomena characterized by sharp amplitude peaks and dips at specific frequencies in the spectra of the waves reflected from periodic surfaces. Theoretical studies proposed the double mode conversion theory, suggesting bulk waves convert to surface waves at periodic rough surfaces and reconvert to bulk waves, which then interfere with specular reflections (main waves) as delayed reflected components (tail waves). However, experimental validation remains incomplete. This study clarifies the relationship between surface waves and tail waves through visualization of wave propagation processes and identifies causes of changes in tail wave formation due to periodic surface geometry. Pulse-echo experiments were conducted using carbon steel specimens with rectangular periodic profiles of varying pitch and depth. Finite-difference time-domain simulations visualized ultrasonic wave propagation under identical experimental conditions. Simulation data showed good agreement with experimental data, validating the simulation approach. Amplitude spectral analysis revealed that the surface waves and tail waves had common frequency characteristics, confirming the double mode conversion assumption. The simulations successfully visualized surface waves generation, propagation, and reconversion to bulk waves, demonstrating tail wave formation from surface waves in detail.

The Laboratoire Vibrations Acoustique is a research unit of INSA Lyon, founded in the late 1960s to study vibrations and their consequences on noise emitted by machines and structures. The aim of this article is to review the historical contributions and main developments of the laboratory over the last fifty years. After examining the early years of the laboratory, the authors retrace the developments and key scientific contributions that have enabled it to gain renown at national and international levels in the field of vibration and acoustical engineering.

Currently, the ultrasonic pulse-echo method is widely used for thickness measurement. To enhance the performance of this technique, this study aims to develop a method to predict the internal geometry of pipes with periodic flaws typically caused by flow-accelerated corrosion. Ultrasonic wave spectra reflected from periodic surfaces show pattern specific characteristics, which we utilized for estimating flaw parameters. We conducted simulations that calculated the propagation of ultrasonic waves reflected on different periodic rough surfaces. These simulations were performed under the same conditions as experiments, which replicated pipe thickness measurement using the pulse-echo method. The simulated pulsed wave amplitude spectra showed the same characteristics as experimental waves when reflected from periodic rough surfaces. For parameter estimation, we trained and tuned a neural network model using only simulation data. To evaluate performance under real-world conditions, we tested the model using experimental data. The results showed relatively high accuracy in estimating flaws depth. While improvements are required, further flaw pitch estimation exhibited potential.

Flow accelerated corrosion generates not only pipe-wall thinning but also roughness on an inside wall. In some flow conditions, the increase in roughness can increase the mass transfer coefficient by up to 80%. It is then very important to have an evaluation tool to monitor and quantify the roughness of a pipe. This study aims to estimate the roughness by using ultrasonic attenuation. The advantage of using ultrasonic attenuation is that it utilizes the signals measured by existing ultrasonic probes, and does not require significant changes to the equipment. To evaluate the inner rough surface, this study compares ultrasonic attenuations on random and periodic rough surfaces. We used an ultrasonic broadband probe on specimens with random and periodic rough surfaces in experiments. The results indicate a significant difference between the attenuation values estimated on random and periodic roughness. In addition, attenuation of amplitude at specific frequencies also was observed. These specific frequencies implied having the potential to estimate the pitch of periodic flaws on the rough surface.

Composites are used in aerospace applications to replace metals and reduce weight. Because of the geometrical complexity and load transfer requirements of such structures, however, composites cannot fully replace metals. Thus, adhesive bonding between metals and composites is useful in such applications. To ensure the safety of these bonds, nondestructive testing and evaluation is required. We propose electromagnetic pulse-induced acoustic testing (EPAT) as a way to evaluate adhesive bonds between composites and metals. Using EPAT, the authors tested two adhesive bonding specimens of metal and CFRP, one with debonding and one without. The two specimens showed different waveforms after the section with debonding, while their waveforms were the same at the start of the measurement before the section with debonding. Thus, EPAT identified the location of debonding.

A 3D finite element modeling approach of ultrasonic propagation combined with a description of the microstructure at the scale of the grains has been implemented. The simulations seek to determine the contribution of scattering to the ultrasonic attenuation in polycrystalline materials. The approach is applied into isotropic microstructures. The ultrasonic propagation is computed with the finite element code ATHENA 3D that developed by EDF. The description of the propagation media accounts for the geometric, elastic and crystallographic properties of coarse-grained material. The attenuation was computed from the decay of simulated multiple backwall echoes. The contribution of the microstructure scattering was isolated by a correction of the attenuation data with the attenuation obtained in an equivalent homogenized material. The simulation investigates the variation of attenuation as a function of several key parameters: grain size, grain orientation, probe frequency.

In many industrial domains, like chemistry, petrochemistry, gaz or water transportation, products are stored for long durations before their delivery. The storage units are submitted to environmental stresses (temperature and humidity variations, corrosion etc.). It is then important to have reliable tools to evaluate their health state and to detect as soon as possible the occurrence of damages. Guided waves methods are good candidates to fulfil these inspections. The guided waves that can propagate on cylindrical structures are multimodal and dispersive. They are generally classified in three families, denoted torsional, longitudinal and flexural modes, according to their polarization. In this paper, we will study the ability of ultrasonic guided modes to detect and localize a lack or an excess of coating on metallic tubes. First of we will study the dispersion curves of an aluminum tube and of a coated aluminum one. From this analysis we will show that the T(0,1) torsional mode is slightly dispersive at a frequency of 100kHz) on the considered structures, and can be used for the considered inspection. Then we will discuss the results of several finite elements method simulations made with Comsol Multiphysics © for the two kind of structures. From the computed data, we will extract B-scans in the timeposition plane. The analyses of these B-scans, allow visualizing the different modes that propagate along the tubes. The influence of a circumferential strip of resin will be shown and discussed. Then after applying a spatial Fast Fourier Transform with sliding window of these B-scans, we get images in the position–wavenumber (z, k) space. It will be shown that this kind of signal processing enables to detect and localize the presence of the resin strip. So the feasibility of an SHM approach based on guided modes is shown for the considered flaw. Finally, we will show how a practical SHM method can be implemented based on the previous results.

Dans de nombreux secteurs industriels, on constate un besoin croissant d’inspecter des parties difficilement accessibles de structures. Il est donc important de mettre en place des moyens d’investigation non destructifs permettant de realiser ce genre de controles. Les ondes guidees repondent a cette problematique et sont grandement utilises pour le suivi de l’etat de sante des structures (barres, plaques, coques, cylindres, etc.). Ces ondes ultrasonores guidees peuvent par exemple etre generees et detectees par des pastilles piezoelectriques (PZT) colles sur la structure a inspecter et excitees en basse frequence sur leur mode de resonance radiale. La reception peut se faire soit avec une autre pastille collee a un autre endroit soit avec la meme pastille emettrice. Dans ce papier, nous montrons la faisabilite de la detection d’un defaut de corrosion (perte d’epaisseur) au moyen de ces ondes guidees sur une barre en acier ferritique de dimensions finies. Dans un premier temps, des simulations par elements finis 2D au moyen du logiciel commercial Comsol Multiphysics sont realisees en utilisant un signal burst de 5 periodes a la frequence de resonance radiale (170kHz) des pastilles utilisees dans les experimentations. A partir des signaux simules une quantification de la profondeur de l’entaille, basee sur des criteres energetiques est proposee. Dans un second temps, les experimentations sont menees dans les memes conditions que les simulations et les memes traitements frequentiels sont realises. Un bon accord simulation/experience est observe et commente, aussi bien en emission/reception sur un seul capteur, qu’en transmission entre deux capteurs. La perte d’epaisseur peut etre quantifiee avec une bonne approximation. Ceci constitue une validation de la simulation qui peut donc etre utilisee pour explorer d’autres types d’interaction mode guide/defaut.

Dans une demarche d’amelioration de la prediction du comportement en glissement d’assemblages boulonnes, des essais de glissement en condition de frottement sec sous chargement statique ont ete realises. Pour cela, une eprouvette en aluminium AU4G non revetu a ete boulonnee a precharge controlee avec une eprouvette en acier inoxydable 316L non revetu. Un chargement transverse a alors ete introduit dans l’assemblage a l’aide d’une machine de traction. Le glissement inter-eprouvette induit et l’evolution de l’effort normal dans l’assemblage ont ete mesures. Les resultats mettent notamment en evidence le phenomene d’instabilite dynamique dit de « stick-slip » (ou de « broutement »). Dans un 1er temps, un etat de l’art des modeles theoriques de frottements disponibles dans la litterature est presente. Le modele dynamique de LuGre a ete selectionne en vue d’une possible utilisation industrielle au sein des methodes de pre-dimensionnement d’assemblages visses actuelles. Dans un second temps, une simulation numerique des essais de glissement est presentee. Le modele correspondant est statique non-lineaire et a ete realise sous Abaqus v6.13. Il est appele a etre ameliore par la suite afin de prendre en compte un maximum de mecanismes physico-mecaniques intervenant dans le phenomene de glissement. Par la suite, les resultats des essais de glissement realises sont presentes. Ils ont permis d’identifier les differents parametres du modele theorique de frottement et sont compares aux resultats issus du modele numerique. En conclusion, les perspectives envisagees a la lumiere de ces premiers resultats sont enoncees.