Research On Numerical Modelling Of Discontinuum Mechanics For Asphalt Mixture

Some early damage phenomenons such as rutting, moisture damage and cracking, which are seriously corrupting pavement service performance, have been drawn significant attentions in recent year. Researches show that these early damages tend to occur in local region, and then spread to other regions. In order to reduce or avoid this kind of damage, the stress condition of local region should be made clear first of all. Although the stress can be measured by experiment accurately, its distribution under multi-component load is difficult to obtain with the limited measurement instruments. Since the continuous mechanics method ignores the discontinuation status of asphalt mixture, the meso-level stress distribution is hardly gotten. The discontinuous computation method is considered advanced to cover the shortage above.Discrete Element Method, Discontinuous Deformation Analysis and Numerical Manifold Method can all be used in discontinuum mechanics numeration. The fundamental principles, advantages and disadvantages are studied in this paper. Through taking into account the characteristic of asphalt mixture (high porosity, loosening particles, coupled of multi materials with large deformation and so on), Numerical Manifold Method provids a good way to satisfy the purpose of computation after detailed comparisons. However, the Numerical Manifold Method is still limited in processing the coordination of displacement and large deformation because of the dependence of mesh. A combination with Mesh-free Galerkin Method is advanced to solve the mechanics problems of asphalt mixture. And remarkable improvement has been gained through this method.Firstly, three key technologies of discontinuous computation method: the generation of computation model, the identification and application of contact, storing and processing format of data are detailed discussed.The generation method of asphalt mixture discontinuum mechanics model named Gradation-Sphere-Precompaction is developed based on the calculation features of Mesh-free Method and Numerical Manifold Method. The controlling of particle graduation, the break-in and pressure of particles, the location of polyhedral model and the generation of asphalt mastic and other issues are outlined.The adoption of Lattice Search and Common Plane method is proved to greatly improve the efficiency in searching contact points. In addition, the sub-contact-matrix in Numerical Manifold Method is reconstituted to merge the Mesh-free method. The scheme is realized for different node with different support nodes.By analysis of discontinuous stiffness matrix, it is concluded that dynamic data compression format is benefit in improving assemble efficiency of the stiffness matrix and reducing the data storage. At the same time, the calculation proves that direct solution procedure guarantees both the precision and speed of computation when the rank of stiffness matrix is not particularly high, and pretreatment iteration method is recommended when the rank is relatively high.Secondly, the realization of Mesh-free Manifold method is focused in this paper. The problems of construction of approximate program, formation of discrete format, transaction of essence boundary and computation format of sub-matrix are indicated. According to the asphalt mixture discontinuous model, the deposit method of material boundary displacement coordinate, the link of asphalt mastic, the search of affection point and the formation of contact blocks and so on are also established. Meanwhile, the precision of this method is also discussed by comparison with finite element method.Finally, the application of Mesh-free Manifold method subjecting the deformation and infuluce of water pressure on asphalt mixture is presented. In order to comparison with the continuous mechanics method result, the corresponding calculation with finite element method is also introduced. Though simple cased is used here, some meaningful conclusions are found as follows:a) The stress distribution of asphalt mixture is closely related to the modulus ratio of stone and asphalt mastic. The stress concentration on stone is found in high ratio, while the stress profile has evenly distribution in low ratio. As a result, to maximize their ultimate strength respectively, the coordinate mechanical status of stone and asphalt mastic could be obtained by adjustment of modulus ratio. The decrease of modules leads to stress distribution balanced inside the particles, but unbalanced between the particles.b) In analysis of Solid-liquid interaction by Euler Equation, the presence of water results in stress decreasing of asphalt mixture internal particles as an additional mass of solid in the mechanic system. But it hardly affects the stress distribution ratio of stone and asphalt.