Jean-François Chaix

Locating and characterizing a crack in concrete with diffuse ultrasound: A four-point bending test

This paper describes an original imaging technique, named Locadiff, that benefits from the diffuse effect of ultrasound waves in concrete to detect and locate mechanical changes associated with the opening of pre-existing cracks, and/or to the development of diffuse damage at the tip of the crack. After giving a brief overview of the theoretical model to describe the decorrelation of diffuse waveforms induced by a local change, the article introduces the inversion procedure that produces the three dimensional maps of density of changes. These maps are interpreted in terms of mechanical changes, fracture opening, and damage development. In addition, each fracture is characterized by its effective scattering cross section.

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

Recent 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.

Quality, Uncertainties and Variabilities

Abstract: Non-Destructive Evaluation (NDE) measurements, carried out in the context of auscultation of concrete structures, aim to either position and calculate the dimensions of a defect or a singularity, or to characterize the reinforced concrete. This book focuses on the characterization of concrete, reinforced concrete and reinforcements. This consists of giving values of the indicators of durability which are usually: – for concrete: compressive strength, modulus of elasticity, porosity, water content and depth of carbonation or contamination by chlorides; – for reinforcements: the corrosion potential and the polarization resistance.

Flaws detection and localization in weld structure using the topological energy method

The non-destructive testing of austenitic welds using ultrasound plays an important role in the assessment of the structural integrity and safety of critical structures in a nuclear reactor. The bedspring and the deck are complex welded structures of very restricted access; the ability to reliably detect and locate defects like cracks is therefore a difficult challenge. Ultrasonic testing is a well-recognized non-invasive technique which exhibits high characterization performances in homogeneous media (steel). However, its capabilities are hampered when operating in heterogeneous and anisotropic austenitic welds because of deviation and splitting of the ultrasonic beam. In order to rise to this important challenge, a model-based method is proposed, which takes into account a prior knowledge corresponding to the welding procedure specifications that condition the austenitic grains orientation within the weld and thus the wave propagation. The topological imaging method implemented is a differential approac...

2D numerical modeling of ultrasonic wave propagation in concrete: A parameterization study in a multiple-scattering medium

Multiple scattering is important when ultrasounds propagate in a heterogeneous medium such as concrete, the scatterer size of which is in the order of the wavelength. The aim of this work is to build a 2D numerical model of ultrasonic wave propagation integrating the multiple scattering phenomena in SPECFEM software. The coherent field of multiple scattering could be obtained by averaging numerical wave fields, and it is used to determine the effective phase velocity and attenuation corresponding to an equivalent homogeneous medium. After the creation of numerical model under several assumptions, its validation is completed in a case of scattering by one cylinder through the comparison with analytical solution. Two cases of multiple scattering by a set of cylinders at different concentrations are simulated to perform a parametric study (of frequency, scatterer concentration, scatterer size). The effective properties are compared with the predictions of Waterman-Truell model as well, to verify its validity.

Nonlinear dynamic acousto-elasticity measurement by Rayleigh wave in concrete cover evaluation

This paper presents local non-destructive evaluation of concrete cover by using surface Rayleigh wave in nonlinear Dynamic Acousto-Elasticity (DAE) measurement. Dynamic non classical nonlinear elastic behavior like modulus decrease under applied stress and slow dynamic process has been observed in many varieties of solid, also in concrete. The measurements conducted in laboratory, consist in qualitative evaluation of concrete thermal damage. Nonlinear elastic parameters especially conditioning offset are analyzed for the cover concrete by Rayleigh wave. The results of DAE method show enhanced sensitivity when compared to velocity measurement. Afterward, this technique broadens measurements to the field.

Ultrasonic wave propagation in heterogeneous solid media

To check up concrete structures “in situ” engineers often employ ultrasonic waves. The implementation of tests and analysis of results even inversion of the problem need good knowledge about propagation phenomena. These phenomena require understanding interaction between ultrasonic waves and scatters, such as granular, porosity, and cracks. This defect can come from fabrication or mechanical damage. The size and the shape of obstacle have an influence on the spatial scattering of ultrasonic waves. We propose to show you the possible using multiple scattering in homogeneous models of propagation and the last work on a sphere in a hard media. Our objective is to bring obstacle geometries closer to the reality. Consequently, we study spheroidal scatters with various aspect ratios.

Study of acoustoelasticity behavior of concrete material under uniaxial compression

The general subject concerns the non destructive testing of pre-stressed structure in civil engineering structures. In this topic we interest in the faisability of stress evaluation in concrete by ultrasonic methods. To do that, we use the acoustoelasticity theory which exploits the nonlinear behaviour of medium to establish the link between stress and ultrasonic velocity. This theory had been validated in homogeneous media and used in steel to evaluated stresses in steel bolt for example. The concrete is a heterogeneous medium where the ultrasonic velocity measurement is more difficult than in steel. The scattered waves induce uncertainty in the measured values but the nonlinear behaviour of concrete is more important than the one of steel. We show an application in high performance concrete submitted to uniaxial compression. We measured velocities of longitudinal and transversal transmitted ultrasonic waves in the direction of the stress and perpendicular to the stress at different stage of the stress test. The sensibilities of the velocities are observed and the potential to evaluate stress in concrete in shown. The prospect concern the widening of formulation tested and the in situ measurements. This study is supported by ANR-ACTENA, a french research program.The general subject concerns the non destructive testing of pre-stressed structure in civil engineering structures. In this topic we interest in the faisability of stress evaluation in concrete by ultrasonic methods. To do that, we use the acoustoelasticity theory which exploits the nonlinear behaviour of medium to establish the link between stress and ultrasonic velocity. This theory had been validated in homogeneous media and used in steel to evaluated stresses in steel bolt for example. The concrete is a heterogeneous medium where the ultrasonic velocity measurement is more difficult than in steel. The scattered waves induce uncertainty in the measured values but the nonlinear behaviour of concrete is more important than the one of steel. We show an application in high performance concrete submitted to uniaxial compression. We measured velocities of longitudinal and transversal transmitted ultrasonic waves in the direction of the stress and perpendicular to the stress at different stage of the stress t...