Exploiting Slow Dynamics Effects for Damage Detection in Concrete

Nonlinear ultrasonic techniques have been developed over the last decades to detect the presence of damage in materials of interest in the field of civil engineering, such as concrete or mortar. The dependence on the strain amplitude of measurable quantities, such as wave velocity, damping factor, resonance frequency, etc. is normally considered a qualitative indicator of the presence of defects at the microstructural level. The experimental approaches proposed have the advantage of being sensitive to small variations in the sample microstructure and are therefore more adapted to detect the presence of small cracks or damaged areas with respect to traditional linear ultrasonic techniques. However, nonlinear methods are difficult to implement, since they usually require a calibrated experimental set-up which also behaves linearly at high amplitudes of excitation. The slow dynamics features, typical of the hysteresis generated by damage, have been given much less attention as a tool for damage detection even though their quantification is often less demanding in terms of an experimental set-up. Here, we provide the first evidence of how recovery, which is part of the slow dynamics process, is sensitive to the presence of damage in concrete samples and thus could be considered as an easy-to-measure nonlinear indicator for Structural Health Monitoring purposes

Time Domain Analysis of Elastic Nonlinearity in Concrete Using Continuous Waves

Concrete and consolidated granular media in general exhibit a strong nonlinear hysteretic elastic behavior when excited by ultrasonic wave perturbations. Due to the sensitivity of their elastic properties to the small changes that can appear in their microstructure, the dynamic stress-strain relationship considered at low strains is affected by the presence of microcracks and hence the progression of damage. Tracking the nonlinear behavior can be made through the dependence on the excitation amplitude of the amplitude of higher order harmonics or of the resonance frequency of the sample. The present chapter shows a time domain analysis of elastic nonlinearity based on the break of the superposition principle when ultrasonic continuous waves are propagating in concrete samples. The latter, which can be of different microstructures (grain sizes, mortar, or polymer matrix), helps to understand the physical mechanisms involved in the different nonlinear elastic responses

Beam shaping to enhance zero group velocity Lamb mode generation in a composite plate and nondestructive testing application

International audienceZero group velocity (ZGV) Lamb modes have already shown their potential in nondestructive testing applications as they are sensitive to the sample structural characteristics. In this paper, we first consider an aluminum sample to validate a method based on the beam shaping of the generation laser. This method is proven to enhance ZGV Lamb modes in aluminum, and then advantageously applied to a composite material plate. Finally, based on the proposed method, scanning the sample over healthy and flawed zones demonstrates the ability to detect subsurface flaws

Passive monitoring of nonlinear relaxation of cracked polymer concrete samples using Acoustic Emission

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Techniques d optique et d acoustique ultra-rapides pour la caractérisation des propriétés des matériaux nano/méso-poreux et des opales synthétiques

Les recherches que nous présentons dans ce mémoire de thèse portent sur la détermination des propriétés élastiques de structures nano et méso-poreuses par ultrasons laser. Des matériaux diélectriques à faible constante de permittivité sont étudiés grâce à un montage pompe sonde. Les résultats sont comparés aux valeurs obtenues par d autres techniques. Des phénomènes d inhomogénéités élastique en profondeur sont discutés. Nous avons par la suite étudié des structures d alumine avec des porosités cylindriques verticales. Des phénomènes de résonances et des signaux interférométriques ont fourni plusieurs paramètres élastiques de cette structure. La dernière partie est consacrée aux opales synthétiques. Les ultrasons laser sont utilisés pour sonder d éventuel modes vibratoires. Certaines corrélations entre les bandes interdites (PBG) et les longueurs d ondes de l excitation/détection du système ont pu être dégagées afin de donner une description qualitative du comportement photonique.In this communication, we present some results of laser ultrasonic experiments on nano and meso porous films and photonic crystals. In the beginning, low-k materials were studied with the pump probe technique. We start by presenting their mechanical and optical properties extracted through analysis of our transient reflectivity results. Our results were compared to data collected by other optical techniques. Some inhomogeneities in the mechanical properties were observed. Secondly, we focused on nano-porous alumina structure. Some resonance phenomena and interferometric measurements helped to determine its elastic properties and dimensions. The last part of this work was allocated to the study of synthetic opals. The pump-probe technique was used to probe the eigenmodes of the submicron spheres. We could also draw some correlations between the photonic band gap (PBG) structure and the excitation/detection wavelength. A qualitative description of their photonic behaviour was formulated.LE MANS-BU Sciences (721812109) / SudocSudocFranceF

Caractérisation acoustique passive du comportement non linéaire des matériaux complexes

International audienceL’émission acoustique (EA) est reconnue pour être une technique efficace de surveillance capable de détecter la création et la propagation de microfissures dans les matériaux structuraux tels que le béton ou les composites lorsqu'ils sont soumis à des contraintes mécaniques. Sur la base de méthodes de traitement de signaux adéquates, différents travaux ont montré le lien existant entre les signatures acoustiques enregistrées et les micro-dommages créés. Par ailleurs, d'autres travaux ont montré la corrélation pouvant exister entre la relaxation non linéaire des matériaux complexes et l'énergie relatives aux endommagements créés au sein de ces mêmes matériaux. Le présent travail propose un protocole expérimental original pour détecter la relaxation non-linéaire d'échantillons de bétons à l'état intact et endommagés. Ce protocole est basé sur le monitoring passif de la relaxation non-linéaire d'échantillons habituellement effectuée à l’aide d’un signal de faible amplitude dans les expériences de dynamique lente. Les résultats montrent la pertinence de la détection passive et révèlent l’existence d’une ‘période de silence’ pendant les premières minutes de la relaxation non-linéaire suite à laquelle les salves d’EA commencent à être détectées. De plus, les caractéristiques des salves d’EA enregistrées pendant la relaxation passive ont montré une nette ressemblance avec celles obtenues pendant l'endommagement des différents échantillons impliquant des mécanismes de cisaillement et de compression

Ultrasonic monitoring of the in-situ polymerization of carbon fiber based thermoplastic composite materials

International audienceComposite materials have grown an increasing interest in the last decade. They present the advantage of reducing weight keeping an excellent weight to strength ratio. These materials found application in various fields such as aerospace, automobile etc. In the aeronautic field, replacing aluminum by carbon fiber based composite (CFC) allows a weight gain of 50 %. On the other hand, CFC has some inconvenience; the relatively high production cost and the process time that reaches few hours. Therefore, the in-situ monitoring of the physical properties, namely mechanical of such structure is of extreme importance. In this communication, we report the results of the monitoring of epoxy resin polymerization during the curing process. An experimental set-up was developed in order to measure in real time the evolution of elastic modulus. Depending on temperature, we could monitor the different phases of the polymerization process from the mechanical point of view. In fact we could observe a three-phase- polymerization process; softening of the material, hardening and finally stabilization of the mechanical properties. On the other hand, acoustic absorption was studied. This parameter exhibit an important change during the phase transition

Caractérisation acoustique passive du comportement non linéaire des matériaux complexes

International audienceL’émission acoustique (EA) est reconnue pour être une technique efficace de surveillance capable de détecter la création et la propagation de microfissures dans les matériaux structuraux tels que le béton ou les composites lorsqu'ils sont soumis à des contraintes mécaniques. Sur la base de méthodes de traitement de signaux adéquates, différents travaux ont montré le lien existant entre les signatures acoustiques enregistrées et les micro-dommages créés. Par ailleurs, d'autres travaux ont montré la corrélation pouvant exister entre la relaxation non linéaire des matériaux complexes et l'énergie relatives aux endommagements créés au sein de ces mêmes matériaux. Le présent travail propose un protocole expérimental original pour détecter la relaxation non-linéaire d'échantillons de bétons à l'état intact et endommagés. Ce protocole est basé sur le monitoring passif de la relaxation non-linéaire d'échantillons habituellement effectuée à l’aide d’un signal de faible amplitude dans les expériences de dynamique lente. Les résultats montrent la pertinence de la détection passive et révèlent l’existence d’une ‘période de silence’ pendant les premières minutes de la relaxation non-linéaire suite à laquelle les salves d’EA commencent à être détectées. De plus, les caractéristiques des salves d’EA enregistrées pendant la relaxation passive ont montré une nette ressemblance avec celles obtenues pendant l'endommagement des différents échantillons impliquant des mécanismes de cisaillement et de compression

Polymer concrete damage characterization using coda wave interferometry (CWI) and linear resonance

International audienceThis work aims to develop an experimental method, which is able to detect the presence of damage in mesoscopic materials using multi-scattered acoustic waves. In particular, we use the coda wave interferometry (CWI) technique in order to detect and locate damage in polymer concrete samples. Concrete samples are locally damaged using quasi-static bending tests. In order to characterize damage, we have experimentally determined nonlinear threshold at resonance (bending resonance modes). Afterward, CWI is applied in the absence and in the presence of the generated linear resonances. Experiments show that CWI doesnt detect any damage even when the excitation level is increased. This result has been confirmed when the acoustic path is parallel and perpendicular to the created bending. However, the presence of linear resonances revealed to be interesting. Indeed, at the same drive levels when CWI is applied simultaneously with the linear resonance, we notice an important sensitivity to damage. Finally, by tracking the effect of damage on the recorded signals along the damaged samples, the proposed original combination offers the possibility to locate damage

Nonlinear Analysis of Damaged Metal-Based Composite Plates Using Guided Waves

International audienceResonance experiments have already proved the high level of nonlinearity in complex materials, including microcracked composites. However, the nonlinear parameters related to elastic modulus and damping are defined around a given resonance mode and are therefore known over a very limited frequency domain. In this contribution, the nonlinear parameters are determined on intact and damaged metal-based composite plates for several flexural resonances. Furthermore, the use of the theoretical formalism corresponding to guided flexural waves allowed to define a nonlinear parameter over a larger frequency domain. Finally, the nonlinear convolution method allowed to take advantage of the harmonics related to the different resonance modes in order to define new nonlinear parameters whose sensitivity is much greater than the ones determined at the fundamental frequencies