586 research outputs found
Présence et écoute du rap en public : une banalisation inachevée
No full textFrançois Debruyne est Maître de conférences en sciences de la communication à l'Université de Lille, et membre du GERIICO. Publications (plus ou moins directement) liées à la proposition de communication : Debruyne F., (2015), « Faire et (se) défaire (d’) une expérience publique de l’écoute », in Culture & Musées, n° 25, p. 69-93. Da Lage E., Debruyne F., (2015), « Les refrains de la mondialisation », in Réseaux, n° 192, p. 115-142. La mondialisation des musiques hip-hop, leur pérennit..
Closed-Loop Optimization of DIC Speckle Patterns Based on Simulated Experiments
No full textStereo digital image correlation (DIC) spreads widely in the last years as one of the most flexible and accurate full-field displacement-strain measurement techniques. The development of novel applications based on DIC makes the design of 3-D setups a challenging task, given the complex and nonlinear nature of stereophotogrammetric methods. The present literature allows the design and optimization of DIC experimental setup only with approximated uncertainty models or upon image quality metrics that are linked loosely with the actual value of uncertainty. In this paper, a closed-loop optimization method based on 3-D experiment simulation is presented. The approach may be used to optimize several parameters (from the camera setup to the DIC processing parameters). This paper features a case study on the problem of optimizing a regular speckle pattern for different measurement tasks. The whole approach is validated experimentally in Section V
An Experimental Investigation on Uncertainty in Measuring Vibration Deflection Shapes with Digital Image Correlation
No full text3-D digital image correlation (DIC) is a widespread full-field displacement measurement technique based on stereo vision. It was formulated to deal with static problems in experimental mechanics in the early seventies, and since then, the applicability of the technique increased due to increasing frame rates and dropping prices of machine vision cameras. As a consequence, DIC became a feasible solution for general-purpose vibration testing. This paper, however, does not offer a comprehensive analysis of DIC accuracy when applied to vibration testing, and therefore, this paper offers a 'Type A' evaluation of uncertainty when measuring vibration deflection shapes with DIC. Uncertainty is evaluated for different experimental conditions on a stepped sine test. Data show that the average value of uncertainty normally lies below 0.02 mm, but in resonant conditions, it can increase up to 0.05 mm (considering a field of view of about half a meter). This demonstrates a strong correlation between the deflection amplitude and the random uncertainty due to motion blur
Effect of DIC Spatial Resolution, Noise and Interpolation Error on Identification Results with the VFM
No full textThe use of experimental tests that involve full-field measurements to characterize mechanical material properties is becoming more
widespread within the engineering community. In particular digital image correlation (DIC) on white light speckles is one of the most used tools,
thanks to the relatively low cost of the equipment and the availability of dedicated software. Nonetheless the impact of measurement errors on
the identified parameters is still not completely understood. To this purpose, in this paper, a simulator able to numerically simulate an
experimental test, which involves DIC is presented. The chosen test is the Unnotched Iosipescu test used to identify the orthotropic elastic
parameters of composites. Synthetic images are generated and then analysed by DIC. Eventually the obtained strain maps are used to identify
the elastic parameters with the Virtual Fields Method (VFM). The numerical errors propagating through the simulation procedure are carefully
characterized. Besides, the simulator is used to compare the performances of DIC and the grid method in the identification process with the
VFM. Finally, the influence of DIC settings on the identification error is studied as a function of the camera digital noise level, in order to find the
best testing configuration.sponsorship: Professor Pierron gratefully acknowledges the support from the Royal Society and the Wolfson Foundation through a Royal Society Wolfson Research Merit Award. (Royal Society, Wolfson Foundation through a Royal Society Wolfson Research Merit Award)status: Publishe
Combining digital image correlation and virtual fields to design an optimized experimental setup for material identification
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Impact of experimental uncertainties on the identification of mechanical material properties using DIC
No full textThis paper is concerned with an in-depth study of the interactions between full-field measurements errors and material identification. It is a further step in a research plan that aims to create a simulation procedure of actual experiments, with the final goal of using the simulator to optimise the test set-up in terms of specimen shape, measurement technique, applied load etc. In particular, here, Digital Image Correlation (DIC) is used as a full-field technique to obtain strain and displacement fields. These maps are used as input in an inverse methodology as, for instance, the virtual fields method (VFM) to obtain the material parameters introducing uncertainties in the characterization. The purpose of this contribution is to bridge the gap between experiments and simulations, in order to obtain predictions as close as possible to reality in terms of identification error. That will be used, as final goal of the general study, to optimize numerically a test set-up configuration, giving a priori the best parameters to use to experimentally identify a specimen. In the present contribute, the operating procedure is to perform real experiments and then to reproduce them numerically. Experimental uncertainties such as noise, lighting conditions, in-plane and out-of-plane motions are treated separately and introduced in the simulator. As such, their impact on the identified material properties can be unambiguously investigated. Here, focus is on the elastic properties of aluminium specimens, i.e. the Young’s modulus and the Poisson ratio and their specific variances due to the aforementioned errors. The simulator predicts reality to a large extent.status: Publishe
Effect of DIC spatial resolution, noise and interpolation error on identification results with the VFM
No full textThe use of experimental tests that involve full-field measurements to characterize mechanical material properties is becoming more widespread within the engineering community. In particular digital image correlation (DIC) on white light speckles is one of the most used tools, thanks to the relatively low cost of the equipment and the availability of dedicated software. Nonetheless the impact of measurement errors on the identified parameters is still not completely understood. To this purpose, in this paper, a simulator able to numerically simulate an experimental test, which involves DIC is presented. The chosen test is the Unnotched Iosipescu test used to identify the orthotropic elastic parameters of composites. Synthetic images are generated and then analysed by DIC. Eventually the obtained strain maps are used to identify the elastic parameters with the Virtual Fields Method (VFM). The numerical errors propagating through the simulation procedure are carefully characterized. Besides, the simulator is used to compare the performances of DIC and the grid method in the identification process with the VFM. Finally, the influence of DIC settings on the identification error is studied as a function of the camera digital noise level, in order to find the best testing configuration
Out-of-Plane motion evaluation and correction in 2D DIC
No full text2D and stereo Digital Image Correlation (DIC) allows to retrieve complex displacement and strain fields on a specimen’s surface. Although 2D DIC is strongly affected by out-of-plane motions, in many situations, it is preferred over stereo DIC because of its ease to use and because only one camera is required. The out-of-plane movements can be ascribed mainly to three causes: the camera positioning, the imperfections of the used test device, and the camera selfheating. These effects gain importance when the distance between the camera and the specimen is reduced. The positioning of the camera aims to have its optical axis perfectly perpendicular to the specimen to observe. Nevertheless small but effective misalignments can easily happen even if suitable devices are used for the alignment. This contribution concerns the experimental evaluation of these movements considering a cyclic uni-axial tensile test performed on an aluminium specimen. The study is particularly focused to the out-of-plane motions that occur at every cycle because of the tensile bench, which are the more critical ones. Finally a compensation method, based on fixed compensation plates, is presented. The method allows to properly correct the data coming from a 2D DIC set-up
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