13th International Conference on Fracture June 16–21, 2013, Beijing, China Modeling Fracture Processes in Numerical Concrete Zhiwei Qian1,2,*, Erik Schlangen2, Guang Ye2, Klaas van Breugel2 1 Materials innovation institute M2i, Delft, the Netherlands 2 Delft University of Technology, Delft, the Netherlands * Corresponding author: z.qian@tudelft.nl Abstract Modeling the fracture processes in concrete requires a material structure of concrete to start with. The material structure of concrete can be obtained either experimentally by X-ray computed tomography, or numerically by a computer simulation. A simplified way to represent the material structure of concrete is to put multiple spheres in a matrix, where the spheres are interpreted as aggregates. This assumption of the shape of aggregates might have influences on the fracture processes in concrete, such as the microcracks propagation path. Recently the Anm material model was proposed and implemented, which can produce a material structure of concrete with irregular shape aggregates. The irregular shape is represented by a series of spherical harmonic coefficients. The further mechanical performance evaluation would benefit from this more realistic material structure. In this paper a material structure of concrete is simulated by the Anm material model. A number of irregular shape particles are planted in a matrix. This material structure is then converted into a voxelized image. Afterwards a random lattice mesh is made, and three types of lattice elements are defined, which represent aggregates, matrix and interface respectively. A uniaxial tensile test is set up and simulated by fixing all the lattice nodes at the bottom of the specimen and imposing a prescribed unit displacement onto all the nodes at the top. The lattice fracture analysis gives the stress-strain response and microcracks propagation, from which some mechanical properties such as Young's modulus, tensile strength and fracture energy can be predicted. Keywords Lattice Fracture, Tensile Test Simulation, Irregular Shape Aggregates 1. Introduction The material structure of concrete determines its global performance. Normal concrete is made from coarse aggregates (e.g. crushed stones, river gravels), fine aggregates (e.g. sands), cement and water. A chemical reaction starts immediately when water is mixed with cement, and reaction products are produced. The resulting cement paste keeps aggregates together and forms a system which is able to carry loads. Mortar consists of cement paste and sand, and concrete is composed of mortar and coarse aggregates. Generally speaking there are two different approaches to obtain the material structure of concrete, which are X-ray computed tomography and computer simulations. From the modeling point of view, the material structure of concrete can be represented by particles embedded in matrix material model. The particles are interpreted as coarse aggregates, and the matrix as mortar. A simplified way to represent coarse aggregates is to use spheres. However this simplification might alter the real material structure of concrete, and thus may change the fracture processes in concrete, such as the microcracks propagation path. Recently the Anm material model was proposed and implemented, which can produce a material structure of concrete with irregular shape aggregates [1]. The irregular shape is represented by a series of spherical harmonic coefficients. The more realistic material structure would make the prediction of fracture processes more precise. Numerical modeling of fracture processes in brittle materials, such as cement paste, mortar, concrete and rocks, started in the late 1960s with the landmark papers of Ngo and Scordelis [2] and Rashid [3], in which the discrete and smeared crack models were introduced. Especially the latter approach gained much popularity, and in the 1970s comprehensive efforts were invested in developing constitutive models in a smeared setting which could reproduce the experimentally -1-
RkJQdWJsaXNoZXIy MjM0NDE=