Papers by Author: Ronald Guillén

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Authors: Manuel François, C. Ferreira, Ronald Guillén
Abstract: The global uncertainty, in X-ray stress analysis, is due to many factors but one of the most important is the uncertainty on peak positions due to counting statistics and other random errors on peak positions. Although a lot of work has been done to estimate the latter, very little work has been devoted to its propagation through the least square regression. This work presents some analytical results in the general case of triaxial stress state (elliptic curve fit) and proposes approximate formulae to easily compute the uncertainty on normal and shear stress components from acquisition parameters such as the number N of y tilts and the maximum y value. It was found that the latter only influences significantly the uncertainty on the normal stress component and that the dependency of the uncertainty on N does not necessarily follow a 1/ N relation.
Authors: Sylvain Fréour, D. Gloaguen, Manuel François, Ronald Guillén, Emmanuel Girard, J. Bouillo
Authors: Sylvain Fréour, Emmanuel Lacoste, Manuel François, Ronald Guillén
Abstract: The scope of this work is the determination of single-crystals elastic constants (SEC) from X-ray diffraction lattice strains measurements performed on multi-phase polycrystals submitted to mechanical load through a bending device. An explicit three scales inverse self-consistent model is developed in order to express the SEC of a cubic phase, embedded in a multi-phase polycrystal, as a function of its X-ray Elasticity Constants. Finally, it is applied to a two-phases (α+β) titanium based alloy (Ti-17), in order to estimate Ti-17 β-phase unknown SEC. The purpose of the present work is to account the proper microstructure of the material. In particular, the morphologic texture of Ti-17 a-phase, i.e. the relative disorientation of the needle-shaped grains constituting this phase, is considered owing to the so-called Generalized Self-Consistent model.
Authors: D. Gloaguen, Emmanuel Girard, Ronald Guillén
Abstract: Complementary methods have been used to analyse residual stresses in zirconium alloy tubes which were manufactured by cold rolling : X-ray diffraction and scale transition model. A modified elasto-plastic self-consistent model (EPSC) has been used to simulate the experiments and exhibits agreement with experimental data. X-ray diffraction analysis in rolling direction shows opposite stress values for {10 14 } and { 2022} planes respectively. The measured strains were generated by an anisotropic plastic deformation. Plastic incompatibility stress on X-ray measurements should be taken into account so as to make a correct interpretation of the experimental data.
Authors: Manuel François, C. Ferreira, Ronald Guillén
Abstract: The results presented in this paper are part of a process to analyse systematically the sources of uncertainty in X-ray stress determination. They concern one part of the effects of temperature variations which could intervene either as random fluctuations or as a monotonic drift during the acquisition. The proposed formulation is in agreement with the recommendations of the ISO guide on the expression of uncertainty (GUM). It was found that the effect is usually negligible for laboratory experiments which are often temperature controlled and for most materials. However the uncertainty can reach 20 MPa for austenitic steels and a temperature drift of 2 K.
Authors: D. Gloaguen, Manuel François, Ronald Guillén, J. Royer
Authors: L. Arnault, S. Branchu, Manuel François, Ronald Guillén, Karim Inal, Jean Lu Lebrun, C. Vial
Authors: Sylvain Fréour, Emmanuel Girard, Ronald Guillén
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