Quantitative linear and nonlinear Resonance Inspection Techniques and Analysis for material characterization: Application to concrete thermal damage.

International audienceDeveloped in the late 80's, Nonlinear Resonant Ultrasound Spectroscopy (NRUS) has been widely employed in the field of material characterization. Most of the studies assume the measured amplitude to be proportional to the strain amplitude which drives nonlinear phenomena. In 1D resonant bar experiments, the configuration for which NRUS was initially developed, this assumption holds. However, it is not true for samples of general shape which exhibit several resonance mode shapes. This paper proposes a methodology based on linear resonant ultrasound spectroscopy, numerical simulations and nonlinear resonant ultrasound spectroscopy to provide quantitative values of nonlinear elastic moduli taking into account the 3D nature of the samples. In the context of license renewal in the field of nuclear energy, this study aims at providing some quantitative information related to the degree of micro-cracking of concrete and cement based materials in the presence of thermal damage. The resonance based method is validated as regard with concrete microstructure evolution during thermal exposure

Applying diffuse ultrasound under dynamic loading to improve closed crack characterization in concrete

International audienceRecent studies show the ability of diffuse ultrasound to characterize surface breaking cracks in concrete. However, derived parameters are sensitive to the presence of partially opened zones along the crack whose pattern may differ from one sample to another. The aim of this letter is to study the variation of diffuse ultrasound parameters while the sample is driven by a low frequency bending load which alternatively opens and closes the crack, allowing to access supplementary information about its morphology. The results show the sensitivity of the method for various crack depths and highlight its potential for concrete nondestructive evaluation

Influence of the depth and morphology of real cracks on diffuse ultrasound in concrete: a simulation study

International audienceThe aim of the present paper is to simulate the propagation of diffuse ultrasonic energy in concrete in the presence of a real crack. The numerical model is presented and validated by the comparison with experimental data from the literature. Unlike most of the studies which consider a crack as a notch, a realistic crack morphology exhibits partial contacts along its lips. These contacts are modeled in order to study their influence on the diffusion parameters. The feasibility of determining the contact density of the crack is shown, revealing practice implications for non-destructive crack sizing and imaging in concrete

Probing material nonlinearity at various depths by time reversal mirrors

International audienceIn this letter, the time reversal mirror is used to focus elastic energy at a prescribed location and to analyze the amplitude dependence of the focus signal, thus providing the nonlinearity of the medium. By varying the frequency content of the focused waveforms, the technique can be used to probe the surface, by penetrating to a depth defined by the wavelength of the focused waves. The validity of this concept is shown in the presence of gradual and distributed damage in concrete by comparing actual results with a reference nonlinear measurement and X ray tomography images

Improving adhesion strength analysis by the combination of ultrasonic and mechanical tests on single lap joints.

International audienceThe aim of this paper is to improve knowledge about adhesion strength in single-lap joints by comparison of data from both Non Destructive Testing (NDT) and standard mechanical tests. study presents a high-frequency ultrasonic imaging of aluminum-epoxy-aluminum joints that carefully chemically prepared using two different surface treatments of the aluminum substrate: silanization and chromic-sulfuric etching. The surface energy of the treated substrate is complete set of ultrasonic data are obtained using high-frequency focused transducers. After inspection, single-lap shear tests were performed, and the mechanical strength of each joint is determined. The good cor relations among the surface measurements, the mechanical tests and ultrasonic results are presented and discussed. The demonstration of a close correlation between ultrasonic images obtained at high frequency and the fracture surface is promising

DIAGNOSTIC D’OUVRAGES HYDRAULIQUES EN TERRE EN MILIEU MARITIME PAR CONTRÔLES NON DESTRUCTIFS ET FUSION DES DONNÉES

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Diagnostic d’ouvrages hydrauliques en terre maritime par Contrôle Non Destructif et fusion des données

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Monitoring microbubbles’ dynamics using a dual modulation method

International audienceAn experimental method for characterizing microbubbles' oscillations is presented. With a Dual Frequency ultrasound excitation method, both relative and absolute microbubble size variations can be measured. Using the same experimental setup, a simple signal processing step applied to both the amplitude and the frequency modulations yields a two-fold picture of microbubbles' dynamics. In addition, assuming the occurrence of small radial oscillations, the equilibrium radius of the microbubbles can be accurately estimated