SUMMARYA modified non-local damage model with evolving internal length, inspired from micromechanics, is developed. It is shown in particular that the non-local influence between two points in the damaged material depends on the value of damage at each of these points. The resulting weight function is nonsymmetric and truncated. Finite element results and strain localization analysis on a one-dimensional problem are presented and compared to those of the original non-local damage model. It is shown that in the course of damage localization, the incremental strain profiles expand according to the modified nonlocal model, instead of shrinking according to the original constitutive relation. Comparisons with experimental data on model materials with controlled porosity are also discussed. Acoustic emission analyses provide results with which the theoretical model is consistent qualitatively. This model also opens the path for durability mechanics analyses, where it has been demonstrated that the internal length in the non-local model should evolve with environmentally induced damage.

International audienceIn this paper, we examine the correlation between the width of the fracture process zone, the parameters entering in the description of size effect (related to the dimension of the specimen especially), and the internal length in non local constitutive relations for a model mortar material with a controlled macro-porosity. Experimental investigations on this material in compression, bending, acoustic emission measurements and their analysis are detailed. The experiments show a good agreement between the evolution of Bažant's size effect parameter d0 and the evolution of the width of the FPZ. The internal length obtained with the help of inverse finite element analysis is also proportional to these quantities. This correlation provides a reasonable approximation of the internal length, from an experimental test on specimens of a single size directly, equipped with acoustic emission localization devices.Dans cet article, nous examinons les corrélations entre la largeur de la zone de microfissuration (FPZ), les paramètres entrant dans la description de l'effet d'échelle et la longueur interne du modèle d'endommagement non local pour un mortier à macro-porosité contrôlée. Des résultats expérimentaux sur ce matériau en comparession, en flexion ainsi que des mesures d'émission acoustiques et leur analyse sont présentés. Les résultats d'essais montrent une bonne corrélation, entre l'évolution du paramètre d0, paramètre de la loi d'effet d'échelle de Bažant, et la largeur de la PFZ. La longueur interne obtenue numériquement par analyse inverse est aussi proportionnelle à ces paramètres. Une bonne approximation de la longueur interne à partir d'essais sur une seule taille d'éprouvette équipée d'un système d'émission, acoustique est aussi obtenue

This paper presents a study on cracking risk due to shrinkage of self-compacting concrete ͑SCC͒. Cracking of SCC was investigated through a comparison of material properties, such as shrinkage, modulus of elasticity, creep, and fracture parameters, between SCC mixtures and ordinary concrete ͑OC͒ mixtures. Restrained shrinkage tests ͑ring tests͒ were also performed on the same mixtures. Numerical simulations were then used to assess the correlation between material properties and results of restrained shrinkage tests. SCC and OC were found to have equivalent shrinkage cracking tendency, provided that compressive strength is kept the same and that SCC has adequate segregation resistance.

In this paper, we examine the correlation between the width of the fracture process zone, the parameters entering in the description of size effect (related to the dimension of the specimen especially), and the internal length in non local constitutive relations for a model mortar material with a controlled macro-porosity. Experimental investigations on this material in compression, bending, acoustic emission measurements and their analysis are detailed. The experiments show a good agreement between the evolution of Bas size effect parameter do and the evolution of the width of the FPZ. The internal length obtained with the help of inverse finite element analysis is also proportional to these quantities. This correlation provides a reasonable approximation of the internal length, from an experimental test on specimens of a single size directly, equipped with acoustic emission localization devices. 1359-5997

SUMMARYA simplified computational technique based on a refined global-local method is applied to the failure analysis of concrete structures. The technique distinguishes the scale of the structure, modelled with large size finite elements, from the scale at which material non-linearity occurs due to progressive cracking and macro-crack propagation. The finite element solution is split into two parts: a linear elastic analysis on a coarse mesh over the entire structure and a non-linear analysis over a small part of the structure where a dense finite element grid is employed. In the non-linear calculation, a non-local damage model is implemented. These two computations are coupled with the help of an iterative scheme. The size and location of the region where a non-linear analysis is performed, is adapted to follow the development of the damage zone. Numerical examples of mode I fracture of concrete specimens with straight and curved cracks are presented.

The serviceability of concrete structures is a coupled problem in which fracture and damage are coupled with several environmental attacks. In this chapter, we start with the investigation of chemo-mechanical damage due to calcium leaching. We show that the fracture characteristics, namely the internal length in continuum models evolve with ageing. This observation is confirmed with experiments on model materials. Acoustic emission data and size effect tests data are strongly correlated with the evolution of the microstructure of the material. This chapter concludes on some creep tests designed to investigate the coupled effect between creep and fracture.

No abstract

No abstract