Numerical Study Of Concrete Under Tension Loading Based On Voronoi Random Aggregate Model In Meso Level

Concrete is a kind of heterogeneous composite material, which is composed of aggregate and cement mortar, because of its rich raw materials, low cost, simple production process and so on, so it is widely used in the field of construction and so on. As one of the most widely used building materials, the tensile strength of concrete is the key factor that affects the whole performance of the concrete structure. With the development of computer science and technology, it is more and more common to study materials at the meso level, and it is easier to reveal the failure mechanism of the materials, which is a good guide for the experimental study. In this paper, the tensile properties of concrete are studied by numerical simulation. Because the polygon(polyhedron) of Voronoi pattern is similar to that of concrete aggregate, the concrete 2D and 3D mesoscopic model using the Voronoi method are established, the influence of aggregate shape and volume fraction on the tensile properties of concrete are studied followed. AThe main work of this paper is as follows:For the Voronoi method to build up a 3D model of concrete, due to the randomness of aggregate shape, the aggregate surface inevitably appears some special small edges and angles, which seriously affects the mesh quality of the finite element model and the convergence of the calculation. By us ing the method of micro cutting of aggregate, and taking into account the external convexity characteristics of the aggregate and the cutting law, to carry out a geometric optimization of the aggregate. Finally, a better grid quality was achieved, which meet the requirements of computational analysis. The standard test piece model of concrete is established and the simulation calculation is carried out, and by the comparison between the calculation results and test results, the reliability of the model was verified.Because of the 2D mesoscopic concrete model possesses the advantages of convenience of the model, fast computation speed, convenient to observe the results. So In this paper, the 2D and 3D meso scale models are established by the above methods. In the 2D meso scale model, the Voronoi polygon aggregate, the circular aggregate and the square aggregate are mainly considered. The corresponding Voronoi polyhedron, the spherical aggregate and the cube aggregate are considered in the 3D meso scale model. From the s imulation results, it can be found that under the action of static tensile stress, the shape of aggregate has little effect on the tensile properties of concrete. The elastic modulus and tensile strength of the concrete model corresponding to the three aggregate shapes are basically the same. According to the comparison of the stress and strain contour, the peak value of stress and strain under the same loading d isplacement is very small, and the distribution of stress and strain is basically the same. Therefore, under the condition of the static tensile stress and adopting the concrete plastic damage model, the aggregate shape has little effect on the tens ile strength of concrete. The interface phase of aggregate and mortar is considered in the two-dimension. The simulation results show that as the interface transition zone in concrete appearance the damage firstly, in the early stage of tensile failure of concrete. And affect the tensile strength of concrete, making the concrete into the softening stage earlier. So it is very important to consider the interface phase of concrete in the study of concrete problems.The influence of aggregate volume fraction on the mechanical behavior of concrete under quasi-static tens ion is studied by using the 2D and 3D meso scale model. The mechanical behavior of concrete uniaxial tens ion with coarse aggregate volume fraction of 22%,33%,41%,53%,62.3% are sets in the 2D Voronoi model. And the coarse aggregate volume fraction of 20%, 40%, 65% are sets in the 2D Voronoi model. The results show that the volume fraction of coarse aggregate in 2D and 3D meso scale model has influence on the tensile strength and elastic modulus of concrete. The volume fraction of coarse aggregate has a great influence on the elastic modulus and tensile strength of concrete, the elastic modulus and tensile strength increase with the increase of the volume fraction of the coarse aggregate.