The Meso Numerical Simulation And The Macro-meso Mechanics Research For Concrete Material

For concrete material, its internal relation between the macro mechanical properties and the meso structure has not been systematically studied. So, in this paper, the meso numerical experiments are carried out firstly. Considering the effect of imperfect interface, the estimate formula of overall mechanical properties and the macro-meso yield criterion of concrete material are established. What's more, the macro-meso constitutive law is also established basing on the nonlinear characteristic of matrix and imperfect bond character of interface. In addition, the effects of micro crack zone on both the impetus and hamper of the macro crack tip are investigated, and the estimate formula of fracture toughness is build up. Finally, the extended finite element method that can simulate the extension of crack without remeshing is researched. This method will exploit a load for the process simulation from damage to fracture. The major studies and conclusion are followed.The three- dimensional meso finite element model has been established by the gradually mesh generated method. And based on the 3-d meso finite element model, all kinds of numerical experiments such as uniaxial tensile test, uniaxial compress test, pseudo triaxial compress tests for different around compress and beam bending test have been made and their failure process are simulated. Numerical experiments are provided to demonstrate that the gradually mesh generated method not only can ensure the request of precision but also can reduce efficiently the compute amount. And the result of meso simulation can offer the analytic gist for grasping the characteristic of concrete material.The hydrostatic stress and the axisymmetric shear stress are respectively applied to the three-dimension meso finite element model, and in terms of the numerical results, the bulk modulus and the shear modulus have been estimated basing on the equivalent with strain potential energy. Accordingly, a numerical estimate method for effective modulo of concrete is offered.Combine the thought of Zhong Z, the principle of superposition is adopted to establish average Eshelby tensor for this case which the interface between the aggregate and the matrix is imperfect bond. And using the established average Eshelby tensor, the Mori-Tanaka estimate method is extended to the overall modulo estimation for imperfect interface case. The relationship of effective modulo with the aggregate percent, the interface softness and the imperfect interface percent is investigated by the new estimate method established. And the conclusion which the effective modulo of concrete increases with the increment of aggregate, but decreases with the increment of interface softness except that effective bulk modulus don't change with the tangent softness is drawn.The concept of energy density support function is extended to the concrete containing the imperfect bond. And a function approach series is constructed to substitute for the energy density support function so that the underivative problem on the yield boundary can be solved. Finally, the meso expression of effective friction coefficient and a macro-meso drucker-prager yield criterion model are established accordingly.A continuous slippery power- exponent function that can reflect soft sect is constructed to describe the nonlinear constitutive law of matrix. And by means of a variational principle proposed by P. Ponte Castaneda, the overall behavior of nonlinear for concrete containing imperfect interfaces is studied. The variational principle proposed by P. Ponte Castaneda involved an optimum problem ultimately. In order to make the optimization successfully, the single variable optimization scheme is adopted by three stages. At the first stage, the matrix of concrete is assumed uncompressible and the constitutive law of concrete containing uncompressible matrix is established by selecting tangent modulo of linear reference matrix. At the second stage, by means of the same scheme as above one, the constitutive law of matrix containing holes is established. Finally, the macro-meso constitutive law of concrete is established by optimize the shear modulo of matrix containing holes based on the above two constitutive law established. And find that concrete contains micro holes is a deep reason why concrete material is of shear dilation property.The principle of superposition and the simple method proposed by M.Kachanov are adopted to study the interaction mechanism between cracks. And find that the maximum interaction effect dose not occur between the cracks when the micro-crack is along or perpendicular to the direction of the maximum tension stress, even some case lead shield effect, which different to the conclusion drawn by M.Ortiz.Strength theory is used to determine the micro crack zone range. And the micro crack is assumed to distribute random. But the direction of micro crack is confirmed with the location of itself. Namely, it is normal to the primary tensor stress. Finally, the interaction effect to the main crack tip produced by the micro-crack zone is researched based on the interaction mechanism between cracks, and the conclusion of the amplification effect to maximal crack tip produced by the micro-crack zone is drawn. The amplification degree increases with the increment of the dense of micro-crack and the length of micro-crack. Whit's more, the effective modulo of micro-crack zone is estimated, and the effective fracture toughness expression is gained from the estimation formula.Basing on the idea of extended finite element method, a class of enrichment displacement function-the exponent discontinuous function is presented to simulate the discontinuous character resulted from discontinuity such as crack or joint. This enrichment function has the vertical distance to discontinuity been the independent variable. It is of exponent attenuation character with the increment of the vertical distance from discontinuity. The numerical experiments are provided to demonstrate that the extension of crack can be simulated successfully without remeshing by the extended finite element method. So the discrete scheme will open a new path for simulation of the whole process from damage to destroy.