Numerical analysis of crack propagation in tension specimens of concrete considered as a 2D multicracked granular composite

A numerical model is presented to study the mechanisms of microcrack propagation in concrete, the load-displacement response and the trajectories of the crack propagation in specimens under displacement control. The microstructure of concrete in this model is represented by a matrix, inclusions and pre-existing microcracks introduced around the inclusions. Both the matrix and the inclusions are assumed to be elastic, homogeneous brittle materials. The stiffness of the inclusions is considered to be three times higher than that of the matrix. Crack propagation in the numerically-generated concrete is controlled by fracture mechanics-based criteria and is calculated through the finite element method. The influence of the microstructure of concrete, the size and the distribution of grains, the properties of the interfacial zone between grains and the matrix, as well as the boundary conditions, on final crack patterns and load-displacement responses are investigated. The different appearance of the numerical load-displacement curves exhibiting the quasi-brittle behaviour observed in experiments is explained in terms of several points of view, especially the dynamic crack propagation.RésuméOn présente un modèle numérique que l’on applique à l’étude des mécanismes de la microfissuration du béton, de la réponse en termes de courbe effort-déplacement et des trajectoires de propagation des fissures dans des éprouvettes en déplacement imposé. La microstructure du béton est représenté par une matrice, des inclusions et des microfissures introduites dans la matrice autour des inclusions. Dans ce modèle, la matrice et les inclusions sont considérées comme étant homogènes, élastiques et fragiles. La rigidité des inclusions est trois fois plus grande que celle de la matrice. La propagation des microfissures dans ce modèle numérique du béton est effectuée selon les critères de la mécanique linéaire élastique de la rupture par la méthode des éléments finis. On étudie l’influence de la microstructure du béton, notamment des auréoles de transition, de la taille et la distribution des grains, ainsi que des conditions aux limites imposées aux éprouvettes sur le trajet des fissures et sur l’allure des courbes effort-déplacement. Les résultats obtenus mettent en évidence le comportement semi-fragile observé lors des essais. Ce comportement a été expliqué par différentes causes et notamment par la propagation dynamique des fissures.

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