Influence of contact interface morphology on the nonlinear interaction between a longitudinal wave and a contact interface with friction : A numerical study

The detection and evaluation of closed cracks are of prime interest in industry. Whereas conventional ultrasonic methods fail to detect these defects, nonlinear methods based on activation of the nonlinear behavior of closed cracks constitute an interesting alternative. The aim of this article is to give a better understanding of interactions between cracks and a longitudinal elastic wave for a quantitative investigation into nonlinear signatures. Using a 1D approach based on the literature, the nonlinear signature of the contact interface is analyzed in two cases. In the first, the interface is initially open and in the second, it is initially closed before interaction with an elastic wave. These signatures were qualitatively observed experimentally in real cracks. Next, in order to investigate the influence of the coexistence of open and closed zones within the interface, a numerical 2D-study is proposed. Two configurations are considered involving two steel blocks in contact, with different contact interface morphologies. The first configuration is a perfectly plane contact interface, while the second one involves an interface between a concave surface and a plane surface. A non-plane wave is also considered. This study attempts to establish a link between local second harmonic generation and interface parameters (pre-stress, gap) that can be exploited for the nondestructive quantitative evaluation of interfaces or cracks

Évaluation des contraintes résiduelles induites par soudage par la méthode ultrasonore : analyse de l'effet de la microstructure

L'utilisation de la méthode ultrasonore pour l'évaluation des contraintes résiduelles repose sur l'effet acoustoélastique qui traduit une dépendance de la vitesse de propagation des ondes acoustiques en fonction de l'état de déformation du solide. Dans le cas du soudage, les modifications microstructurales observées dans la zone affectée thermiquement et dans la zone fondue induisent également des variations de la vitesse de propagation des ondes acoustiques. La superposition des deux effets : contraintes et microstructure conduit à surestimer les niveaux de contraintes. Ce travail réalisé en collaboration avec le CETIM de Senlis essaie d'apporter une réponse à ce problème observé dans le cas du soudage. La solution adoptée consiste à caractériser l'effet acoustoélastique ainsi que les vitesses de propagation $V_{0 }$ pour les différentes zones de la soudure. L'étude expérimentale effectuée sur des tôles en aciers P460 HLE et P265 soudées avec un chanfrein en X a permis de valider notre démarche. Ceci nous permet d'envisager sous certaines conditions, l'utilisation de cette méthode dans le cas des équipements sous pression

Assessment of Long-Range Guided-Wave Active Testing of Storage Tanks

International audienceAbstract Guided Wave Testing (GWT) is now increasingly being used for the non-destructive testing of large structures. Petrochemical tank bottoms are particularly subject to corrosion. Today, the monitoring of corrosion in storage tanks is probably one of the most challenging applications of GWT because of the size and the complexity of such medium. This article deals with the main physical issues of this application, in particular, the prediction of the elastic field propagating in the tank wall and bottom, and the prediction of guided wave scattering by joints. Drawing on current research work, a representative numerical configuration is defined. The global diffusive effect and the local diffraction effect of the lap joints are studied. The methodology have led us to focus on the low ultrasound frequency range: from 10 to 50 kHz. A quantitative evaluation of the scattering by lap joint is carried out by means of simulations and experiments on elementary reduced scale joints. Dynamic range computations make it possible to get prior knowledge about the minimum signal-to-noise ratio (SNR) required to get information about the tank bottom, for a given configuration, leading to a SNR-resolution trade-off. The method can be extended to larger tanks. The results confirm that the use of GWT technology for long-range active testing and imaging of storage tanks is promising

Contribution of non-destructive methods for residual and applied stress assessment

International audienceThe knowledge of the stresses in the materials is an important factor in understanding the mechanical state of the components and to guarantee their stability over time. Such knowledge may be used to predict the deformations at machining, the dimensional stability over time, and the fatigue strength. The knowledge of pre-load stress in bolted joints enables to avoid the loosening and guaranty the fatigue behavior of the assembly. In introduction, the presentation briefly explicates the interest and limitations of residual stress measurement methods such as X-ray diffraction and incremental hole drilling-the latter is not totally non-destructive-. These methods are often referred to as the reference surface residual stress measurement method. Then, the presentation will first consist in the description of principles of Non-Destructive Methods as ultrasound and ferromagnetic noise (Barkhausen noise), which represent two experimental methods used for residual stress assessment. Finally, various applications of the use of non-destructive methods for residual stress measurement, lead in CETIM, or described in the literature, will be described, as follows:-the use of electromagnetic methods as Barkhausen noise and combined electromagnetic methods (such as "3MA", for surface stress on bearings,-the use of ultrasonic compressional critical waves (LCR) for surface stress on welded plates-the use of a combination of compressive and shear ultrasonic waves to control the stress on already tightened bolts, without loosening, thanks to electromagnetically coupled ultrasonic transducers Recent developments of these methods now allow on-site measurements, including the X-ray diffraction method, and we will also present some trends and evolutions of non destructive assessment of residual stress, as laser ultrasonic stress assessment, described in the literature

Pipe two-phase flow non-invasive imaging using Ultrasound Computed Tomography: A two-dimensional numerical and experimental performance assessment

International audiencePipe two-phase flow non-invasive imaging is of great interest in the field of industry. In particular, small bubble flow imaging through opaque pipes is challenging. Ultrasound computed tomography can be a relevant technique for this purpose. However, perturbation phenomena that are inherent to the configuration (acoustic impedance mismatching, circumferential propagation, reverberation) limit two aspects: the performance of the technique and the use of conventional inversion algorithms. The objectives of the presented work are: (i) to predict the effects of the pipe wall on ultrasonic waves for both metallic and plastic pipe, (ii) to define a consistent inversion algorithm taking into account those effects, (iii) to validate and to assess the limitations of the designed imaging numerical tool using an experimental setup. The benchmark configuration consists of 150 mm diameter 3 mm thick pipes containing 6 mm diameter rods acting as reference scatterers. Two materials of very different acoustical properties were tested: aluminum and PMMA. The results highlighted that the quality of the reconstructed image is very dependent on the pipe material. The results showed that, using an adapted inversion model, consistent target reconstruction is obtained. Based on numerical predictions, performance limitations are reached for metallic pipes

Assessment of qualitative and quantitative S 0 guided wave tomography of sharp thickness loss defects in the isotropic membrane regime

International audienceProgress in instrumentation, computer hardware, and inversion methods is encouraging the development of more advanced guided wave tomography techniques, especially for nondestructive testing of plate structures to characterize corrosion. An experimental S0 tomography performance assessment in the membrane regime is reported. One of the main interests of the fundamental membrane regime is that in this regime, waves are propagated over long distances. A 2 mm thick steel disk containing calibrated sharp artificial defects (flat bottom holes) is tested in both reflection and extinction modes. A reconstruction algorithm derived from the membrane approximation is presented. We expose a complete reflection mode inversion approach that includes beam inversion, waveform deconvolution, and thickness loss calibration. Non-linear correction factors are introduced and discussed for quantitative imaging. A width-regularity-depth description of defects is introduced to put the results into perspective with other defect geometries. The results show the relevance of the inversion method to enhance the imaging performance with regard to defect localization and sizing. Crucial points concerning instrumentation such as coupling, signal-to-noise ratio, excitation mode, coupling, selection of frequency, are also discusse

Tomographie ultrasonore tridimensionnelle de composants mécaniques

International audienceNon-destructive testing techniques now enables to represent the response of the objects in the form of an image, in particular in ultrasonics. In the case of ultrasound, this image consists in a presentation of the amplitudes or time of flight of the waves in the material. Ultrasonic imaging thus allows the objects to be represented in the form of a projection parallel or perpendicular to the surface of the material, as in B-scan used in medicine. Tests carried out to date in various laboratories as well as CETIM show that it is now possible to perform 2D or 3D ultrasonic tomography as in X-ray tomography, More, such type of reconstruction is applicable in guided wave tomography for plate imaging. So, ultrasonic tomography gives us an access to mechanical properties of the material under scan. The communication will consist in describing the problem of the ultrasound tomographic control by reconstruction, and to position this method in relation to the existing processing methods (Full Matrix capture, FTP). Analogies with the x-rays, and the particularities of the ultrasound reconstruction, will be explained, highlighting the advantages and limitations of each method. Results obtained by CETIM in low frequency imaging of a pipe section content will be presented, first in term of density. More, the tomographies performed showed that the time-of-flight reconstruction enables to monitor the evolution of volume temperature distribution of a flow circulating in the same pipe. First results obtained by CETIM in guided wave ultrasonic tomography of pipe walls will be presented too. Finally, the major potential applications of reconstruction tomography will be discussed, as well as the latches to be lifted in order to allow industrialization of this process, while considering the three-dimensional ultrasonic imagery in the context of the development of digital and computer technologies

Analysis of the longitudinal critically refracted waves (Lcr) acoustic field applied to residual stress measurement

International audienc