Browsing by Author "Cordero, RR"

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    Assigning probability density functions in a context of information shortage
    (2004) Cordero, RR; Roth, P
    In the context of experimental information shortage, uncertainty evaluation of a directly measured quantity involves obtaining its standard uncertainty as the standard deviation of an assigned probability density function (pdf) that is assumed to apply. In this article, we present a criterion to select the appropriate pdf associated with the estimate of a quantity by seeking that pdf which is the most probable among those which agree with the available information. As examples, we apply this criterion to assign the proper pdf to a measurand assuming that we know just its estimate, or both its estimate and its standard uncertainty. Our results agree with those obtained by applying the principle of maximum entropy to both situations.
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    The uncertainty of experimental derivatives
    (2004) Lira, I; Cordero, RR; François, M; Vial-Edwards, C
    A procedure is presented to evaluate the uncertainty of derivatives computed from polynomial curves or surfaces fitted to experimental data. The procedure takes into account the uncertainties in the dependent and independent variables and agrees with international recommendations. It is valid independent of the experimental technique from which data are obtained. The application of the procedure is demonstrated by evaluating the uncertainty of strains calculated by differentiation of whole-field displacement data obtained by moire interferometry.
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    Uncertainty analysis of displacements measured by phase-shifting Moire interferometry
    (ELSEVIER SCIENCE BV, 2004) Cordero, RR; Lira, I
    Phase-shifting Moire interferometry is a whole-field optical technique used to measure displacements. Because of its high sensitivity, its results are affected by even small environmental perturbations. In this paper, the influences of these perturbations are characterized and compared with other systematic effects. The experiment was a uniaxial tensile test. In-plane displacement measurements were performed several times under repeatability conditions at different load stages. The dispersions of these results were evaluated by their standard deviations, which showed fluctuations at twice the fringe frequency. An uncertainty analysis was carried out to include other systematic effects. We found that the local displacement uncertainties depended on the sample elongation and on the reference location. An equation was found for these uncertainties as a function of the total number of fringes occurring. (C) 2004 Elsevier B.V. All rights reserved.
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    Uncertainty evaluation of displacements measured by electronic speckle-pattern interferometry
    (2004) Cordero, RR; Martínez, A; Rodríguez-Vera, R; Roth, P
    We have applied electronic speckle-pattern interferometry (ESPI), a whole-field optical technique, to measure the displacements induced by applying tensile load on a metallic sheet sample. because we used a dual-beam ESPI interferometer with collimated incident beams, our measurements were affected by errors in the collimation and in the alignment of the illuminating beams of the optical setup. In this paper, the influences of these errors are characterized and compared with other systematic effects through an uncertainty analysis. We found that the displacement uncertainty depends strongly on the incidence angles of the illuminating beams of the interferometer. Moreover, faults in the alignment of the incident beams have more influence on the uncertainty than errors in their collimation. The latter errors change the incident beams from collimated to slightly divergent, modifying in turn the interferometer sensitivity. We found that this sensitivity change can be generally neglected. (C) 2004 Elsevier B.V. All rights reserved.
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    Whole-field analysis of uniaxial tensile tests by Moire interferometry
    (ELSEVIER SCI LTD, 2005) Cordero, RR; Francois, M; Lira, I; Vial Edwards, C
    Moire interferometry-a high sensitivity whole-field optical technique-was used to follow the evolution of the deformation process of an aluminium sample subjected to a uniaxial tensile test. This technique allowed us to measure the two in-plane displacement components undergone by the sample, to evaluate the strain, stress and rotation fields, and to appreciate the trends in the deformation pattern that characterized the different stages of the test. Through a subtraction process between fields obtained at two different load levels, we were able to identify the area where strains began to localize and to observe the appearance of the diffuse neck. (c) 2004 Published by Elsevier Ltd.
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    Whole-field strain uncertainty evaluation by a Monte Carlo method
    (2004) Cordero, RR; Roth, P
    In this work, we used a Monte Carlo computer simulation to evaluate the uncertainties of the strains obtained from a displacement field measured by moire interferometry. The displacements were induced by applying tensile load to a metallic sheet sample. At each point of the illuminated area, the strain standard uncertainty was taken as the standard deviation of the series of outcomes obtained by a large number of strain evaluations. These strain evaluations were performed by differentiating the surfaces that were fitted to the sets of points in the space formed by the two spatial coordinates of the field and the corresponding local displacement. These sets of points were generated according to the probability density functions that we considered appropriate. The reported procedure to evaluate the strain uncertainty is valid independently of the interferometric technique used to measure the displacement field.