The Mesoscopic Numerical Simulation Of The Failure Process Of Concrete Specimen In The Static And Dynamic Loads

Due to more research in concrete mechanical properties and rapid development of computer technics in recent years, more and more attentions are paid to combining the concrete test with numerical simulation to study the physical and mechanical properties of concrete, while the heterogeneity and characteristics of local damage of concrete can be more effectively reflected through numerical model on the mesoscopic scale. Based on the numerical random aggregate model, which can model the real concrete, the results from the mesoscopic numerical simulation are mainly depend on two aspects; 1) element failure criteria and degradation rules of stiffness matrix; 2) the selection of mesoscopic material parameters.Similar in the generation and the real concrete of concrete aggregate model based on the failure process of concrete materials, the micro can be reasonably numerical results, on the one hand depends on how to select and determine the unit element stiffness matrix failure criteria and degradation rules; On the other hand depends on the microscopic material parameters of the selected cell. Meanwhile, due to the large number of micro units, select the appropriate method to improve computational efficiency is also a need to address the problem.In this paper, concrete is taken as a three-phase composite material consisting of matrix, aggregate and interfaces between them; a meso damage FEM program is developed to simulate the macro-level mechanical properties. Specifically, the study includes:(1) To reflect the actual situation of the concrete, the numerical model of random concave and convex aggregates is established. In this process, on the one hand, odd-shaped aggregate particles is removed by the extreme ratio threshold, on the other hand, after filling, an interative adjustment process is performed to remove the overlaps between adjacently grains. The filling efficiency and success rate are ensured, and the random shape and distribution of aggregrate are also considered.(2) For the simulation of concrete macro stress-strain softening curve, based on the simple elastic damage constitutive laws, the selection of concrete meso element parameters is discussed. Compared with separately considering the random distribution of elastic modulus and strength, more reasonable tension-compression damage curve of concrete specimen is obtained by utilizing the product of the strength and elastic modulus as integrated random parameter of the meso-element.(3) By the above material generation method, the numerical simulation of concrete specimen under uniaxial loads are studied. Based on the derived stress-strain curves and crack evolution chart, the concrete damage and fracture process are analysised. Tensile and pressure-shear numerical tests are carried on the concrete specimens with precast cracks, and the tensile fracture and shear fracture process are obtained. Then single aggregate concrete specimens is established, the influence of interface strength to the macro-strength is discussed, while the shape of aggregate on the crack extension is investigated. On the basis of single and two aggregrate specimens, the most likely crack propagation path of concrete is numerically simulated.Finally, the mechanical properties of concrete specimen under dynamic displacement uniaxial load are studied.