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Enhanced features of a constitutive equation gap identification method for heterogeneous elastoplastic behaviours
Auteur(s): Madani T., Monerie Y., Pagano S., Pelissou C., Wattrisse B.
(Article) Publié:
Advanced Modeling And Simulation In Engineering Sciences, vol. 4 p. (2017)
Ref HAL: hal01667738_v1
DOI: 10.1186/s4032301700921
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Résumé: To identify mechanical properties in heterogeneous materials, the local stress fields have to be estimated. The recent developments in imaging techniques allow reachingprecise and spatially dense kinematic fields (e.g. displacement, strain ...). In this paper,an iterative procedure is used to identify the distribution of elastoplastic materialparameters and the local stress fields. The formulation and the principle of the methodare briefly presented while attention is paid to check its reliability and efficiency onfinite element simulation data as reference fullfield measurements. The method is alsoapplied to noisy measured displacement fields to assess its robustness.




Metrological Analysis of the DIC Ultimate Error Regime
Auteur(s): Bornert Michel, Doumalin Pascal, Dupré JeanChristophe, Poilane Christophe, Robert Laurent, Toussaint Evelyne, Wattrisse B.
Conference: 1st Annual International Digital Imaging Correlation Society (Philadelphia, US, 20161107)
Actes de conférence: International Digital Imaging Correlation Society, Conference Proceedings of the Society for Experimental Mechanics Series.  ISBN 9783319514383, vol. p.p.191193 (2017)
Ref HAL: hal01633706_v1
DOI: 10.1007/9783319514390_45
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Résumé: In DIC, the “ultimate error regime” corresponds to situations for which the shape function used to describe the material transformation perfectly matches the actual one. We propose to confront results obtained from numericallyshifted images with the predictions of theoretical models developed in the literature to describe bias and random error evolutions with respect to the imposed displacement. Results show the overall good predictions of these models but small deviations arise, mainly around integer values of imposed displacements for noisy images. These deviations are interpreted as the unrepresentativeness of the underlying hypotheses of the theoretical models in these particular cases.



Shortcut in DIC error assessment induced by image interpolation used for subpixel shifting
Auteur(s): Bornert Michel, Doumalin Pascal, Dupré JeanChristophe, Poilâne Christophe, Robert Laurent, Toussaint Evelyne, Wattrisse B.
(Article) Publié:
Optics And Lasers In Engineering, vol. 91 p.124133 (2017)
Ref HAL: hal01620034_v1
DOI: 10.1016/j.optlaseng.2016.11.014
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3 citations
Résumé: In order to characterize errors of Digital Image Correlation (DIC) algorithms, sets of virtual images are often generated from a reference image by inplane subpixel translations. This leads to the determination of the wellknown Sshaped bias error curves and their corresponding random error curves. As images are usually shifted by using interpolation schemes similar to those used in DIC algorithms, the question of the possible bias in the quantification of measurement uncertainties of DIC softwares is raised and constitutes the main problematic of this paper. In this collaborative work, synthetic numerically shifted images are built from two methods: one based on interpolations of the reference image and the other based on the transformation of an analytic texture function. Images are analyzed using an inhouse subsetbased DIC software and results are compared and discussed. The effect of image noise is also highlighted. The main result is that the a priori choices to numerically shift the reference image modify DIC results and may lead to wrong conclusions in terms of DIC error assessment




Viscoinertial regime of immersed granular flows
Auteur(s): Amarsid L., Delenne J.Y., Mutabaruka P., Monerie Y., Perales Frédéric, Radjai F.
(Article) Publié:
Physical Review E, vol. 96 p. (2017)
Ref HAL: hal01607197_v1
DOI: 10.1103/PhysRevE.96.012901
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Résumé: By means of extensive coupled molecular dynamics–lattice Boltzmann simulations, accounting for grain dynamics and subparticle resolution of the fluid phase, we analyze steady inertial granular flows sheared by a viscous fluid. We show that, for a broad range of system parameters (shear rate, confining stress, fluid viscosity, and relative fluidgrain density), the frictional strength and packing fraction can be described by a modified inertial number incorporating the fluid effect. In a dual viscous description, the effective viscosity diverges as the inverse square of the difference between the packing fraction and its jamming value, as observed in experiments. We also find that the fabric and force anisotropies extracted from the contact network are well described by the modified inertial number, thus providing clear evidence for the role of these key structural parameters in dense suspensions.




Scaling behavior of immersed granular flows
Auteur(s): Amarsid L., Delenne J.Y., Mutabaruka P., Monerie Y., Perales Frédéric, Radjai F.
Conference: International Conference on Micromechanics of Granular Media (Powders & Grains) (Montpellier, FR, 20170703)
Actes de conférence: , vol. 140 p. (2017)
Ref HAL: hal01594573_v1
DOI: 10.1051/epjconf/201714009044
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Résumé: The shear behavior of granular materials immersed in a viscous fluid depends on fluid properties (viscosity, density), particle properties (size, density) and boundary conditions (shear rate, confining pressure). Using computational fluid dynamics simulations coupled with molecular dynamics for granular flow, and exploring a broad range of the values of parameters, we show that the parameter space can be reduced to a single parameter that controls the packing fraction and effective friction coefficient. This control parameter is a modified inertial number that incorporates viscous effects.




Terahertz thermometry system to measure temperature in the thickness of a solid polymer
Auteur(s): Poulin Cyndie, Triki Meriam, Bousmaki Karim, Duhant Alexandre, Louche H., Wattrisse B.
(Article) Publié:
Quantitative Infrared Thermography, vol. p. (2017)
Ref HAL: hal01583910_v1
DOI: 10.1080/17686733.2017.1362791
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Résumé: This paper deals with thermal attenuation of a transmitted THz signal (165 GHz) across a POM polymer sample subjected to a thermal gradient in the thickness direction. The paper describes the experimental setup, including a THz sensor, a system to impose thermal loading and an infrared camera used to measure temperature variations at the surface. The thermal dependence of the transmitted THz signal through the sample was studied along a spatial profile. A simple polynomial model, validated through finite element analysis and thermal imaging measurement, was used to estimate temperature variations in the thickness direction. The correspondence between the 2D transmitted THz signal and the 3D temperature distribution allowed us to estimate the thermal sensitivity of the absorption coefficient in the THz range. This study showed that the THz sensor was sensitive enough to measure THz signal variations due to small temperature variations. The mean temperature may be determined along the thickness direction once the thermodependence of the transmission and reflection coefficients are known.




Assessment of Digital Image Correlation Measurement Accuracy in the Ultimate Error Regime: Improved Models of Systematic and Random Errors
Auteur(s): Bornert Michel, Doumalin Pascal, Dupré JeanChristophe, Poilâne Christophe, Robert Laurent, Toussaint Evelyne, Wattrisse B.
(Article) Publié:
Experimental Mechanics, vol. p. (2017)
Ref HAL: hal01577239_v1
DOI: 10.1007/s1134001703285
Exporter : BibTex  endNote
Résumé: The literature contains many studies on assessment of DIC uncertainties, particularly in the ultimate error regime, when the shape function used to describe the material transformation perfectly matches the actual transformation. For pure subpixel translations, bias and random errors obtained for experimental or synthetic images show more complex evolution versus the fractional part of displacement than those predicted by the existing theoretical models. Indeed, small deviations arise, mainly around integer values of imposed displacements for noisy images, and they are interpreted as the unrepresentativeness of the underlying hypotheses of the theoretical models. In a first step, differences between imposed and measured displacements are analysed: random error is independent of fractional displacement, and systematic error does not decrease for values close to integer displacements whatever the noise level. Therefore, new prediction models are proposed based on the analysis of identified phenomena from synthetic specklepattern 8bit images. The statistical approach used in this paper generalizes the methods proposed in the literature and mimics the experimental methodology usually used for displacement measurements performed in different subsets in the same image. Two closedform expressions for the systematic and random errors and a linear interpolation scheme are developed. These models, depending only on image properties and the imposed displacement, are built with a very limited number of parameters. It is then possible to predict the evolution of bias and random errors from one to four images.

