Sub-minute in situ Fracture Test in a Lab CT-scanner

International audienceThe present study aims at demonstrating the feasibility of performing a fracture test in less than one minute in a lab CT scanner despite the severe time constraints of tomography acquisition. After introducing the basic concepts of Projection-based Digital Volume Correlation (P-DVC), the specific implementation of this methodology to a wedge splitting test on a refractory material is presented. The kinematics of the test is described over a mesh tailored to the sample geometry, and the elastic behavior of the sample is exploited through finite element computations to provide sensitivity fields of experimental boundary conditions to allow for their "measurements." Enhancing the simulation to account for crack advance with extended finite element analyses allows the sensitivity of the procedure to the crack position to be assessed. A confidence interval for the refractory toughness is finally obtained

Simple renormalizable flavor symmetry for neutrino oscillations

pre-printThe recent measurement of a nonzero neutrino mixing angle θ13 requires a modification of the tri-bimaximal mixing pattern that predicts a zero value for it. We propose a new neutrino mixing pattern based on a spontaneously broken A4 flavor symmetry and a type-I seesaw mechanism. Our model allows for approximate tri-bimaximal mixing and nonzero θ13, and contains a natural way to implement low- and high-energy CP violations in neutrino oscillations, and leptogenesis with a renormalizable Lagrangian. Both normal and inverted mass hierarchies are permitted within 3σ experimental bounds, with the prediction of small (large) deviations from maximality in the atmospheric mixing angle for the normal (inverted) case. Interestingly, we show that the inverted case is excluded by the global analysis in 1σ experimental bounds, while the most recent MINOS data seem to favor the inverted case. Our model make predictions for the Dirac CP phase in the normal and inverted hierarchies, which can be tested in near-future neutrino oscillation experiments. Our model also predicts the effective mass |mee| measurable in neutrinoless double beta decay to be in the range 0:04 ≤ |mee| ≤ 0:15 eV for the normal hierarchy and 0:06 ≤ |mee| ≤ 0:11 eV for the inverted hierarchy, both of which are within the sensitivity of the next generation experiments

Modal characterization of crack network development in an MgO containing refractory castable

International audienceDamage due to MgO hydration in castables has been studied by bar resonance and recently by Digital Image Correlation (DIC). The hydration reaction kinetics was studied via principal component analyses (PCA) applied to DIC results of images acquired during 60 h of curing and drying of an MgO containing refractory castable. The experiment was carried out in a in-house climatic chamber at 50 • C and 50% of relative air humidity. The displacement and maximum eigen strain fields were obtained via DIC. Their PCA revealed the crack network as the most relevant component, with a temporal development of a sigmoidal curve where a two-parameter Weibull law was satisfactorily fitted. The reaction duration was virtually identical for both fields, and only a time shift in reaction initiation and saturation was attributed to the choice of field. The approach allows the need for user-defined thresholds to be avoided for crack quantification

On accounting for speckle extinction via DIC and PCA

International audienceDigital Image Correlation (DIC) is a full-field measurement technique that generally relies on brightness conservation principles. This work aims to analyze cases in which the speckle pattern vanished after heating, thereby severely altering the brightness. Sets of images acquired during \textcolor{red}{\bf 6} experiments were registered and then used to obtain optimal sets of reference images for each time step via Principal Component Analysis (PCA). The proposed methodology significantly reduced the gray level residuals and provided insight into brightness variations that occurred in the analyzed cases. It was possible to study cases with severe speckle pattern changes by updating the reference image when standard DIC did not converge and using the PCA methodology to obtain optimal reference states

Calibration of cohesive parameters for a castable refractory using 4D tomographic data and realistic crack path from in-situ wedge splitting test

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