Browsing by Author "Roth, P"

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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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    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 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.