Search

The homogenized elastic properties of polycrystals depend on the grain morphology and crystallographic orientations. For simplification purposes, the orientations of the grains are usually considered three independent Euler angles. However, experimental investigations reveal spatial correlations in these angles. The Karhunen–Loève expansion is used to generate random fields of Euler angles having exponential kernel functions with varying correlation lengths. The effective elastic moduli for numerically generated statistically equiaxed cubic polycrystals are estimated via the classical Eshelby–Kröner Self-Consistent homogenization model. The influence of the correlation lengths of the orientations' random fields on the statistical properties of the effective elastic moduli has been investigated. Our results show that spatially correlated Euler angles could increase the variability of the homogenized elastic properties compared to the ones having uncorrelated Euler angles. Nevertheless, using independent random variables for Euler angles remains valid when correlation lengths are close to the average grain size. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the relevance of the diffusion parameters identified on kinetics whose saturation levels are unknown. Two types of diffusion kinetics have been considered: a Fickian and a non-Fickian kinetics. Numerical experiments, based on the generation of noisy data corresponding to reference values of diffusion parameters, have been carried out. The two models used in this study are Fick's model and the «Dual-Fick» model. Identification procedures were then applied on these data sets, truncated at different critical times. In the specific case of Dual Fick kinetics, the classical least square method was compared to an alternative approach based on the piecewise analysis of the shape of the diffusion curves. The identified parameters may deviate significantly from the expected reference values when the truncation threshold of the data set precedes the steady state. Also, these inaccurate parameters impact the predictions of global water uptake, water concentration profiles and stresses gradients through the thickness of the sample. [ABSTRACT FROM AUTHOR]

In this work, a study on the influence of morphologic texture on the residual stress determination by diffraction in metallic materials with cubic and hexagonal symmetry is proposed. To this end, elastic self-consistent model has been developed to properly take into account the morphologic texture. Extreme crystallites morphologies (sphere, disc and fibre) were studied, and coupled with the crystallographic texture to reflect the combined effect of morphologic and crystallographic texture in elasticity. In the case of morphologic texture, a stronger influence than the crystallographic texture on the estimated residual stresses (several tens of MPa difference) was observed. We propose a methodology through a scale transition model to take into account the influence of these different morphologies in the stress analysis by diffraction methods. The main purpose of this work was to make the best choice for lattice planes ( hkl) used for residual or internal stress analysis, in elasticity, depending on the morphologic (and crystallographic) texture of the polycrystal, especially when the usual X-ray Elasticity Constants (XECs) are used instead of the stress factors. [ABSTRACT FROM AUTHOR]