No abstract

SUMMARYWe present a meso-scale model for failure of heterogeneous quasi-brittle materials. The model problem of heterogeneous materials that is addressed in detail is based on two-phase 3D representation of reinforced heterogeneous materials, such as concrete, where the inclusions are melt within the matrix. The quasibrittle failure mechanisms are described by the spatial truss representation, which is defined by the chosen Voronoi mesh. In order to explicitly incorporate heterogeneities with no need to change this mesh, some bar elements are cut by the phase-interface and must be split into two parts. Any such element is enhanced using both weak and strong discontinuities, based upon the Incompatible Mode Method. Furthermore, a dedicated operator split solution procedure is proposed to keep local any additional computation on elements with embedded discontinuities. The results for several numerical simulations are presented to illustrate the capabilities of the proposed model to provide an excellent representation of failure mechanisms for any different macroscopic loading path.

International audienceThis paper presents a Finite Element model for the modeling of the failure of heterogeneous material at the meso-scale. This model is cast into the framework of the Enhanced Finite Element Method (E-FEM). Two kinds of enhancement are performed: (1) in the displace-ment field (strong discontinuity approach) in order to take into account micro-cracks, (2) in the strain field (weak discontinuity) in order to take into account heterogeneities without any mesh adaptation. Mechanical applications (uniaxial tension and compression loading, non-proportional loading) are performed in the context of cementitious materials such as concrete. We show the capability of the model to represent some of the main features of such materials observed at macro-scale

One of the main objectives of the APPLET project was to quantify the variability of concrete properties to allow for a probabilistic performance-based approach regarding the service lifetime prediction of concrete structures. The characterization of concrete variability was the subject of an experimental program which included a significant number of tests allowing the characterization of durability indicators or performance tests. Two construction sites were selected from which concrete specimens were periodically taken and tested by the different project partners. The obtained results (mechanical behavior, chloride migration, accelerated carbonation, gas permeability, desorption isotherms, porosity) are discussed and a statistical analysis was performed to characterize these results through appropriate probability density functions

International audienceIn this work, we discuss a novel anisotropic constitutive model of plasticity, which can be used to replace the classical phenomenological models for composite materials, like concrete, with marked difference of behavior in tension and compression. The model is constructed from fine scales by making use of the corresponding meso-scale representation of concrete distinguishing aggregate from cement paste. The elastic response and failure mechanisms at this scale are represented by the corresponding unstructured mesh of truss elements, which is shown to be capable of representing a number of fine features of inelastic response, such as the statistical isotropy of elastic response placed in-between the stringent Hashin-Shtrikman bounds, the pronounced difference of behavior in tension and compression, the sensitivity of bi-axial compression strength to the volume fraction of aggregate and the bi-axial fracture energy corresponding to each particular mode of failure. The results of this kind obtained with meso-model are then packed within a new meso-scale model with these enhanced features, which can be used to successfully replace the standard phenomenological models of concrete in ultimate state computations of complex structures providing increased predictive capabilities

In view of the significant impact of thin scale heterogeneities in regards with the macroscopic response of concrete (and generally speaking of heterogeneous materials), a particular effort is dedicated to morphological representation and modeling. The development of a model based on spatially correlated random functions (Random Fields) is proposed in this article. It is shown how the stationary ergodic property coupled with the spatial structure of correlated Random Fields can efficiently address the problematic when submitted to a threshold process. Recent mathematical results Adler (2008) give accurate ways to analytically control the resulting morphology, both geometrically and topologically speaking. The generalized aspect of this framework has to be seen here as the ability of the model to represent different kind of morphologies such as matrix/inclusion, opened or closed porosity. With such features, heterogeneous material can be represented at different scales. By expanding a rather abstract formula given by Adler (2008), the authors aim at spreading this point of view with a "ready for use" framework. Furthermore, by addressing common issues such as, reaching high volume fraction with disconnected topologies and representing grain size distributions, solutions to adapt it to cementitious materials are given.

No abstract

International audienceA two-scales numerical analysis is set up in order to upscale the permeability of fractured materials such as concrete. To that aim, we couple finite element (FE) kinematics enhancements (strong discontinuities) representing fine scale cracks to the fine scale permeability tensor. The latter may be split into two parts: the first one is isotropic and corresponds to flows within the porosity of the material; the second one, based upon a set of cracks with different orientations and openings, is anisotropic. For the latter, each crack is a path for mass flow according to the Poiseuille law considering two infinite planes. We show how the upscaling procedure leads both to the definition of macroscopic permeability tensors as well as the flow rate evaluation for components of concrete structur