Contribution à la caractérisation non destructive des milieux complexes : Ultrasons diffus et non-linéarité

This manuscript presents a synthesis of my research works since my hiring at the Aix en Provence Technological University Institute, ES&H department, in 2008 as a “maître de conferences” (Assistant Professor). My activities were conducted at the Laboratory of Non Destructive Evaluation, affiliated to the Laboratory of Mechanics and Acoustics (LMA CNRS UPR 7051) in 2012. Presented works concern nondestructive evaluation of heterogeneous media such as concrete, bubbly liquids, biological cells… and find new applications to nuclear energy, aeronautics or medicine. Major achievements are related to the nonlinear dynamical behavior of these mediums for which the output data is not anymore proportional to the input, as well as their multiple scattering properties occurring when the wavelength is in the order of the microstructural scales. Nonlinear phenomena, whose physics is not completely established yet, are leveraged to assess parameters which are highly sensitive to microstructural changes in the presence of damage. Several methods including nonlinear resonance and time reversal are presented. Multiple scattering phenomena are leveraged and simplified into a simple diffusion equation similar to heat diffusion. This concept is employed to characterize macro cracks in concrete structures. Prospective studies are presented through several research projects.Ce mémoire présente un résumé de mes recherches, effectuées depuis mon recrutement en tant que Maître de Conférences en 2008 au département Hygiène Sécurité Environnement de l’IUT d’Aix. Elles ont été conduites au Laboratoire de Caractérisation Non Destructive d’Aix, rattaché au Laboratoire de Mécanique et d’Acoustique (LMA CNRS UPR7051) en 2012. Les travaux présentés concernent la caractérisation non destructive des milieux hétérogènes comme le béton, les bulles, les cellules… avec des applications nouvelles pour l’industrie nucléaire, l’aéronautique ou la médecine. Les avancées majeures concernent le comportement dynamique non linéaire de ces milieux dont l’information de sortie n’est pas proportionnelle à la consigne d’entrée, ainsi que la propagation des ondes en milieu multi-diffusant apparaissant lorsque la longueur d’onde correspond aux grandeurs caractéristiques de la microstructure. Les phénomènes non linéaires dont la physique n’est pas encore complètement établie sont mis à profit pour évaluer des paramètres qui s’avèrent très sensibles à l’évolution de la microstructure en présence d’endommagement. Plusieurs méthodes dont la résonance et le retournement temporel sont présentées. Les phénomènes de diffusion multiple sont mis à profit et simplifiés par une équation de diffusion semblable à celle de la chaleur. Ce concept est utilisé pour caractériser des macro-fissures dans les structures en béton. Les perspectives de ces travaux sont déclinées à travers plusieurs sujets de recherches potentiels

Fast and slow dynamics in a nonlinear elastic bar excited by longitudinal vibrations

Heterogeneous materials, such as rocks and concrete, have a complex dynamics including hysteresis, nonlinear elasticity and viscoelasticity. It is very sensitive to microstructural changes and damage. The goal of this paper is to propose a physical model describing the longitudinal vibrations of this class of material, and to develop a numerical strategy for solving the evolution equations. The theory relies on the coupling between two processes with radically-different time scales: a fast process at the frequency of the excitation, governed by nonlinear elasticity and viscoelasticity; a slow process, governed by the evolution of defects. The evolution equations are written as a nonlinear hyperbolic system with relaxation. A time-domain numerical scheme is developed, based on a splitting strategy. The numerical simulations show qualitative agreement with the features observed experimentally by Dynamic Acousto-Elastic Testing

Dynamic acousto-elastic test using continuous probe wave and transient vibration to investigate material nonlinearity

This study demonstrates the feasibility of the dynamic acousto-elastic effect of a continuous high frequency wave for investigating the material nonlinearity upon transient vibration. The approach is demonstrated on a concrete sample measuring 15 15 60 cm3 . Two ultrasonic transducers (emitter and receiver) are placed at its middle span. A continuous high frequency wave of 500 kHz propagates through the material and is modulated with a hammer blow. The position of the hammer blow on the sample is configured to promote the first bending mode of vibration. The use of a continuous wave allows discrete time extraction of the nonlinear behavior by a short-time Fourier transform approach, through the simultaneous comparison of a reference non-modulated signal and an impact-modulated signal. The hammer blow results in phase shifts and variations of signal amplitude between reference and perturbed signals, which are driven by the resonant frequency of the sample. Finally, a comprehensive analysis of the relaxation mechanisms (modulus and attenuation recovery) is conducted to untangle the coupled fast and slow hysteretic effects. 2016 Elsevier B.V. All rights reserved.The authors want to acknowledge the financial support of the Ministerio de Economia y Competitividad (MINECO), Spain and FEDER funding (Ondacem Project: BIA 2010-19933). J.N. Eiras is grateful to the Ministerio de Economia y Competitividad (MINECO), Spain, Grant BES-2011-044624 and Grant EEBB I-15-10178, in support of an extended visit to the Aix-Marseille Universite. The French National Research Agency is also thanked for support under the EVADEOS (Grant ANR-11-VILD-0002) and ENDE (Grant ANR-11 RSNR 0009) programs.Eiras Fernández, JN.; Vu, QA.; Lott, M.; Paya Bernabeu, JJ.; Garnier, V.; Payan, C. (2016). Dynamic acousto-elastic test using continuous probe wave and transient vibration to investigate material nonlinearity. Ultrasonics. 69:29-37. doi:10.1016/j.ultras.2016.03.008S29376

Effect of water saturation and porosity on the nonlinear elastic response of concrete

International audienceNonlinear interaction of a monochromatic elastic wave with a low frequency should be a good tool for non-destructive evaluation of existing concrete structures. Nonlinear indicators have already proved efficient in detecting global damage by exhibiting a significant sensitivity regarding classical linear ultrasonic methods like wave speed or attenuation. However, it is necessary to understand the influence of some structural parameters such as porosity, stress state, or water saturation on the nonlinear processes. In this way, a recent model containing all of these potential contributors is presented in this paper. It is sustained by nonlinear interaction experiments in impact mode. This method reveals a great potential for in situ measurements with a low frequency propagating into the whole structure. We make use of a calibrated concrete sample's series, conditioned at different water saturation states, to quantify the influence of water content and porosity on the nonlinear response of concrete

Experimental Investigation on the Compressive Stress-Sensing Ability of Steel Fiber-Reinforced Cement-Based Composites under Varying Temperature Conditions

This study investigates the piezoresistive (self-sensing) properties of short stainless-steel fiber-reinforced mortar under varying temperature conditions. Different reinforced mortars were produced by varying fiber and aggregate content. First, Electrical Impedance Spectroscopy (EIS) measurements were used to characterize the electrical properties of the mortar specimens. EIS measurements were performed at temperatures of 24 °C, 35 °C, and 50 °C. Second, to investigate the self-sensing capacity of the different composites, the fractional changes of electrical impedance at 1 kHz were monitored under two conditions: temperature variation alone (cooling down from 35 °C or 50 °C to room temperature), and temperature variation combined with cyclic compressive loading (up to 5 MPa). The results of the former were used to compensate for the effect of temperature variations in the latter. Both temperature and mechanical loading produced meaningful variations in the electrical impedance and piezoresistivity of the investigated composites. Conclusions are drawn with respect to the stress and temperature sensitivity of the composites. The real and imaginary parts of the electrical impedance of the mortar produced with the highest fiber volume fraction (0.01%) and higher aggregate content (volume fraction of 60%) were distinctly sensitive to temperature and stress, which suggests the possibility of using the same composite as a stress and temperature sensor

Caractérisation par acoustique non-linéaire des dégradations du marbre sous l’effet de cyclages thermiques pour la conservation du patrimoine

Certaines œuvres en marbre exposées aux conditions environnementales se trouvent dégradées dans le temps. Ces dégradations pourraient être induites par l’effet des cyclages thermiques, même à des faibles niveaux (40-60°C). La compréhension des mécanismes mis en jeu est essentielle pour développer des méthodes de conservation adaptées. La caractérisation et la compréhension de ces mécanismes de dégradation sont réalisées à partir d’expériences de laboratoire sur des échantillons de marbre de Carrare calibrés et subissant des cycles contrôlés en température. Le suivi de l’évolution des paramètres mécaniques des échantillons est effectué de manière non destructive par spectroscopie ultrasonore à résonance non linéaire, NRUS. Les paramètres suivis sont plus précisément la fréquence propre, le facteur de qualité et le facteur de non-linéarité. Des observations à l’échelle microscopique (lames minces, microtomographie X) sont réalisées pour mettre en évidence les mécanismes impliqués (ouverture de joints de grain, microfissuration, etc)

Caractérisation non destructive du béton (étude du potentiel de l'acoustique non linéaire)

Cette thèse étudie le potentiel des techniques issues de l acoustique non linéaire appliquées à la caractérisation non destructive du béton. Les méthodes non linéaires ont été envisagées car les indicateurs de non linéarité montrent des dynamiques d évolutions importantes face à l endommagement dans les milieux homogènes. Souvent, leur dynamique d évolution est de dix fois supérieure à celle des paramètres linéaires. Un des enjeux majeurs pour l évaluation non destructive dans le domaine du génie civil, est la recherche d indicateurs capables de fournir des informations pertinentes in situ. Le béton, matériau de structure, voit ses caractéristiques évoluer au cours du temps en fonction des paramètres structuraux (composition, endommagement ) et environnementaux (teneur en eau, température, précontrainte ). Milieu fortement hétérogène et microfissuré par nature, il exhibe un comportement fortement non linéaire caractéristique des matériaux appelés non classiques , mis en évidence dans les années 1990 pour les roches ou plus récemment les milieux granulaires. Dans un premier temps, nous nous attachons à caractériser la non linéarité classique du béton, traduisant la dépendance de la vitesse des ondes ultrasonores avec la contrainte appliquée. Pour ce faire, nous transposons au cas du béton une méthode issue de la géophysique fondée sur l analyse de la coda des signaux transmis, au fort potentiel d application in situ. Nous nous intéressons dans un second temps à la sensibilité des indicateurs non linéaire non classiques à un endommagement thermique progressif. Nous employons pour ce faire la méthode de résonance non linéaire et montrons la sensibilité de ces indicateurs à ce type d endommagement. Nous montrons de plus la faisabilité de l analyse des modes de résonance transverses pour la méthode ainsi que la similitude de leur réponse avec celle des modes longitudinaux. Nous traitons enfin des limites de transposition sur site de cette méthode. Nous avons développé une autre approche au fort potentiel de transposition in situ, en étudiant la non linéarité par l interaction d un impact mécanique avec une onde monochromatique. Nous examinons enfin l apport d un modèle proposé récemment, permettant de traduire l influence de certains paramètres tels que la porosité et la teneur en eau sur la réponse non linéaire du béton. Nous transposons ce modèle au cas du béton, puis nous appuyant sur une série d expériences, nous proposons une fonction permettant d optimiser les paramètres influents du modèle. Nous avons démontré le potentiel des méthodes non linéaires pour l auscultation in situ du béton. Les travaux se poursuivront sur la possibilité d augmenter la sensibilité de détection des non linéarités en mettant en œuvre le retournement temporel et la dynamique lente.This thesis study the potential of nonlinear acoustics based techniques applied to non-destructive evaluation of concrete. Nonlinear based methods have been considered as regard of nonlinear indicators sensitivity face homogeneous medium s damage. Their dynamic evolution is often two order magnitude greater than linear ones. One of the greater stacks for non destructive evaluation in civil engineering is research of indicators capable of providing relevant information in situ. Concrete, structural material, find itself properties altering in time as function of its structural (composition, damage ) and environmental (water saturation, temperature, pre-stress ) parameters. Naturally highly heterogeneous and micro-cracked medium, it exhibits a strong nonlinear response, signature of so called since 1990 s non classical materials such as rocks or more recently as granular mediums. We illustrate first the classical nonlinearity of concrete, reflecting ultrasound wave speed dependence with quasi-static stress. Thus, we apply in case of concrete a method from geophysics studying the coda of transmitted waves, with a high potential for on site applications. Secondly, we study sensitivity of nonlinear non classical parameters face of a progressive thermal damage. So we employ the Nonlinear Resonant Ultrasound Spectroscopy (NRUS) method and show sensitivity of these indicators to this kind of damage. We then show feasibility and sensitivity of applying shear modes for the method as well as similarity of their response with compressional ones. At last, we deal with its on site transposition limits. Another approach is implemented studying non classical nonlinearity by interaction of a mechanical impact with a monochromatic wave, with a high potential for on site applications. We finally describe and transpose in case of concrete, a recent modelling which allow describing the influence of some parameters as water saturation and porosity on the nonlinear response of concrete. We then exploit a battery of experiments in order to optimising some influent parameters in the model. We have demonstrated the potential of nonlinear methods for on site non destructive evaluation of concrete. This work is to be continued by studying possibilities of increasing sensitivity of nonlinearities detection by using time reversal mirror or slow dynamics.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Micro-bubbles cloud's spectroscopic nonlinear coefficient measurements towards its characterization

International audienceIn 4th generation nuclear reactors cooled with liquid sodium, argon microbubbles are present in the primary sodium. Due to the opacity of liquid sodium, acoustic control methods are chosen for operating inspections. However, this bubble presence greatly affects the acoustical properties of the medium. In bubbly liquids, nonlinear propagation can arise at very low amplitudes and therefore affect the viability of ultrasonic measurements. The spectroscopic measurement of the nonlinear parameter is therefore required to estimate the reliability of acoustics measurements. Moreover, adding nonlinear information to attenuations and celerity measurements could improve bubble distribution estimation and provide more reliability on very low void fractions measurements. A dynamic acoustic-elastic testing method is employed to measure the nonlinear parameter over a large bandwidth. Inversion of these measurements is performed with success