Novel anisotropic continuum-discrete damage model capable of representing localized failure of massive structures. Part II: identification from tests under heterogeneous stress field

In Part I of this paper we have presented a simple model capable of describing the localized failure of a massive structure. In this part, we discuss the identification of the model parameters from two kinds of experiments: a uniaxial tensile test and a three-point bending test. The former is used only for illustration of material parameter response dependence, and we focus mostly upon the latter, discussing the inverse optimization problem for which the specimen is subjected to a heterogeneous stress field.Comment: 18 pages, 12 figures, 6 table

Digital Image Correlation technique: Application to early fatigue damage detection in stainless steel

In the context of development of a numerical model, to accurately predict the fatigue life of a structural component, it is fundamental to consider both the initiation stage and the propagation stage of micro-cracks. Such a development requires dedicated experimental tools both to provide the physical understanding needed for designing models and to validate the proposed approaches and models. Thus, this paper presents the experimental means that need to be used for such a purpose. The approach is based on the analysis of displacement field measurements by digital image correlation (DIC) during low-cycle fatigue tests. A specific filtering tool is also presented to minimize the committed errors when derivative operation is performed for strain calculation. Therefore, in this quite recent application of DIC, the reproducibility of the method has to be questioned and validated, with help of some more conventional strain measurements devices. It seems that the experimental conditions have to be carefully controlled, so that the results can be interpreted in terms of mechanical phenomena

Asymptotic analysis based modeling of small inhomogeneity perturbation in solids: two computational scenarios

International audienceThe presented work is a step towards designing a numerical strategy capable of assessing the nocivity of a small defect in terms of its size and position in the structure with low computational cost, using only a mesh of the defect-free reference structure. We focus here on presenting two computational scenarios allowing to efficiently evaluate flaw criticality. These scenarios are considering either the effect of a fixed flaw for any evalutaion point in solid, or varying flaws on a fixed evaluation point. 1 Motivation, introduction and problem definition The role played by defects in the initiation and development of rupture is crucial and has to be taken into account in order to realistically describe the behavior till complete failure. The difficulties in that context revolve around (i) the fact that the defect length scale is much smaller than the structure length scale, and (ii) the random nature of their position and size. Even in a purely deterministic approach, taking those defects into consideration by standard models imposes to resort to geometrical discretisations at the defect scale, leading to very costly computations and hindering parametric studies in terms of defect location and characteristics. Our current goal is to design an efficient two-scale numerical strategy which can accurately predict the perturbation in terms of stress caused by an inhomogeneity in elastic (back-ground) material. To make it computationally efficient, the analysis uses only a mesh for the defect-free structure, i.e. the mesh size does not depend on the (small) defect scale. We consider a linearly elastic body occupying a smooth bounded domain Ω ⊂ R d (with the spatial dimensionality d = 2 or 3), whose boundary Γ is partitioned as Γ = Γ D ∪Γ N support a prescribed traction ¯ t and a prescribed displacement ¯ u, while a body force density f is applied in Ω. On the basis of this fixed geometrical and loading configuration, we consider two situations, namely (i) a reference solid characterized by a given elasticity tensor C, which defines the background solution u, and (ii) a perturbed solid constituted of the same background material except for a small inhomogeneity whose material is characterized by C , which defines a perturbed solution u a. The aim of this work is to formulate a computational approach allowing to treat case (ii) as a perturbation of the background solution (i), in particular avoiding any meshing at the small inhomogeneity scale. This will be achieved by applying known results on the asymptotic expansion of the displacemen

Asymptotic analysis based modeling of small inhomogeneity perturbation in solids: two computational scenarios

International audienceThe presented work is a step towards designing a numerical strategy capable of assessing the nocivity of a small defect in terms of its size and position in the structure with low computational cost, using only a mesh of the defect-free reference structure. We focus here on presenting two computational scenarios allowing to efficiently evaluate flaw criticality. These scenarios are considering either the effect of a fixed flaw for any evalutaion point in solid, or varying flaws on a fixed evaluation point. 1 Motivation, introduction and problem definition The role played by defects in the initiation and development of rupture is crucial and has to be taken into account in order to realistically describe the behavior till complete failure. The difficulties in that context revolve around (i) the fact that the defect length scale is much smaller than the structure length scale, and (ii) the random nature of their position and size. Even in a purely deterministic approach, taking those defects into consideration by standard models imposes to resort to geometrical discretisations at the defect scale, leading to very costly computations and hindering parametric studies in terms of defect location and characteristics. Our current goal is to design an efficient two-scale numerical strategy which can accurately predict the perturbation in terms of stress caused by an inhomogeneity in elastic (back-ground) material. To make it computationally efficient, the analysis uses only a mesh for the defect-free structure, i.e. the mesh size does not depend on the (small) defect scale. We consider a linearly elastic body occupying a smooth bounded domain Ω ⊂ R d (with the spatial dimensionality d = 2 or 3), whose boundary Γ is partitioned as Γ = Γ D ∪Γ N support a prescribed traction ¯ t and a prescribed displacement ¯ u, while a body force density f is applied in Ω. On the basis of this fixed geometrical and loading configuration, we consider two situations, namely (i) a reference solid characterized by a given elasticity tensor C, which defines the background solution u, and (ii) a perturbed solid constituted of the same background material except for a small inhomogeneity whose material is characterized by C , which defines a perturbed solution u a. The aim of this work is to formulate a computational approach allowing to treat case (ii) as a perturbation of the background solution (i), in particular avoiding any meshing at the small inhomogeneity scale. This will be achieved by applying known results on the asymptotic expansion of the displacemen

Modélisation de l'effet de taille dans les nanocomposites par la méthode EFEM (Embedded Finite Element Method)

International audienceAvec l'utilisation croissante des nanocomposites, la nécessité de développer des procédures de modélisation efficaces apparaît. Les modélisations issues de la mécanique des milieux continus introduisent cet effet de taille par la prise en compte d'une élasticité de surface à l'interface entre les nano-inclusions et la matrice. Afin de contourner les limites en termes de géométrie des inclusions associées aux modélisations analytiques, nous proposons ici une stratégie numérique basée sur la méthode Embedded FEM pour prédire le comportement mécanique des matériaux nano-renforcés, y compris en prenant en compte des comportements non linéaires pour les différentes phases. Mots clés : Nanocomposite, FEM, Élasticité surfacique, Effet de taille