Browsing by Author "Francois, M."

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    Analysis of plastic strain localization by a combination of the speckle interferometry with the bulge test
    (ELSEVIER SCI LTD, 2007) Montay, G.; Francois, M.; Tourneix, M.; Guelorget, B.; Vial Edwards, C.; Lira, I.
    The process of localization of strains, diffuse and localized necking, up to fracture in equi-biaxial loading was analyzed through the images obtained by electronic speckle pattern interferometry (ESPI). The problem of localization is important in the sheet metal forming processes. The ESPI technique is used to have a better resolution on the measured strains (10(-5)) than other technique such as the image correlation (10(-2), 10(-3)). The bulge test is currently used to determine the mechanical properties of materials by measuring the deformation that occurs in response to the application of a controlled pressure. This test is used to determine the mechanical properties of sheet metals submitted to an equi-biaxial loading path, the strains at failure are used as data to determine forming limit diagrams (FLDs).
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    Strain and strain rate measurement during the bulge test by electronic speckle pattern interferometry
    (ELSEVIER SCIENCE SA, 2007) Montay, G.; Francois, M.; Tourneix, M.; Guelorget, B.; Vial Edwards, C.; Lira, I.
    This paper presents a new experimental method to measure the strain increment and the strain rate during the bulge of a copper sheet. The electronic speckle pattern interferometry (ESPI) is combined with the bulge test to measure the field of strain increment. The strain rate is used to detect heterogeneity in the strain distribution.
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    Uncertainty of residual stresses measurement by layer removal
    (PERGAMON-ELSEVIER SCIENCE LTD, 2006) Bendek, E.; Lira, I.; Francois, M.; Vial, C.
    A model to evaluate the uncertainty in the measurement of the through-thickness residual stress distribution in plates by the layer removal technique is presented. Thin layers were chemically etched from a stripe on rectangular specimens cut from a low carbon cold-rolled steel sheet. Phase shifting laser interferometry was used to measure the ensuing curvature. Polynomials were least-squares adjusted to the curvatures as a function of the etched depth. The polynomials were inserted into an integro-differential equation relating the curvature to the residual stresses, which were assumed to be a function of depth only. A comparison with X-ray diffraction measurement of the surface residual stresses showed good agreement. The uncertainty was found to increase steeply at the surfaces and to depend mainly on the assumed value for the modulus of elasticity, on the curvature fit, and on the depth of etching. (C) 2006 Elsevier Ltd. All rights reserved.