Study On The ?-? Mixed-mode Damage And Fracture Mechanism Of Concrete Based On The Random Aggregate Distribution

Because of the high heterogeneity of concrete composites,there are a number of micro-defects and micro-cracks in concrete before the loading process.The evolution of these initial defects determines the ultimate macro-fracture path of concrete.In view of the common ?-? mixed-mode damage and fracture phenomena in concrete structures,concrete is regarded as a composite material consisting of coarse aggregate,mortar and pore,and the damage and fracture mechanism of which were studied at the meso-scale in the paper.On the basis of meso-scale mechanics and damage mechanics,concrete is regarded as a three-phase composite material consisting of aggregate,mortar and pore in the paper.Taking the meso-scale ?-? mixed-mode concrete damage and fracture characteristics as the main research content,the anti-symmetrical loading test method of four-point shear was used to test the precast notched concrete trabecula.The effects of the volume fraction and specific surface area of coarse aggregate under different stress conditions on the damage fracture morphology,fracture characteristics and load-carrying capacity of concrete under ?-? mixed-mode are discussed.At the same time,the equivalent damage constitutive model of concrete three-phase meso-scale composites was analyzed based on the equivalent method of multi-phase composites,and the two-dimensional random polygon meso-scale aggregate numerical model of concrete equivalent to the three-dimensional aggregate parameters was generated by Monte Carlo Simulation method.Considering the influence of the internal pore of concrete on its fracture properties,polygonal pore with a total area of 5% mortar was generated by the same method.Based on this,a two-dimensional meso-scale numerical model of concrete was established,and the numerical simulation of concrete ?-? mixed-mode damage and fracture model was carried out by using the displaying dynamic algorithm.The accuracy of the meso-scale numerical model and the feasibility of the meso-scale equivalence method in the study of concrete ?-? mixed-mode damage and fracture are verified by comparing the results of damage and fracture test and numerical simulation.The Random Aggregate Model not only reflects the heterogeneity of concrete meso-structure,but can simulate the random crack development process of concrete ?-? mixed-mode damage and fracture.At the same time,the results of experiment and numerical simulation show that the meso-level inhomogeneity of concrete has a significant impact on its macro-mechanical properties.The four-point bending beam numerical simulation method for studying the fracture properties of concrete is an efficient and convenient method to obtain relatively accurate and reasonable test results through a small number of test models.