Numerical Simulation Of Meso-scale Concrete Cracking Under Load

The research of heterogeneous characteristics of concrete materials has always been one of the hot spots in the field of civil engineering,especially in the meso level,the concrete is regarded as a three-phase composite material composed of aggregate particles,mortar matrix and interface layer.Combined with the analysis method of numerical simulation,the internal micro cracks,porosity and other initial defects of concrete are studied on the whole concrete material.The influence of mechanical properties.It is important to study the change of internal structure on the micro level to judge and predict the fracture damage behavior on the macro level of concrete,which plays an important role in optimizing the mechanical properties of concrete materials.In this paper,from the point of view of meso numerical model,the basic mechanical parameters such as the elastic modulus of three-phase materials are determined by experiments,which verify the high consistency between the numerical simulation results and the experimental results,and reflect the whole damage and fracture process of the concrete specimen in the numerical simulation,and appropriately modify the model parameter variables to explore the impact of internal material property changes on the macro performance of concrete.In this paper,the efficiency of numerical model element division is also considered.Combined with the idea of equivalent element,the traditional random aggregate model is transformed into the element equivalent model.The redevelopment of ABAQUS subroutine is carried out and SDV7 damage variable output module is compiled.The advantages and disadvantages of different simulation methods are studied by comparing the results of uniaxial tension and uniaxial compression of the model The main research work is summarized as follows:(1)This paper introduces the basic concepts and applications of damage mechanics and fracture mechanics as well as the relationship between them,and expounds the calculation model of equivalent elastic modulus and double broken line damage model based on the idea of equivalence.(2)The idea and method of Monte Carlo are applied to the aggregate distribution of random aggregate model,and MATLAB programming language is compiled to realize the random generation and random placement of aggregate,and the generated aggregate is processed to generate a three-phase random aggregate geometric model with interface layer.(3)According to the code for design of mix proportion of ordinary concrete JGJ55-2011,the pure mortar specimens and concrete specimens with different sizes were prepared.The axial compression failure test was carried out and the mechanical performance parameters such as modulus of elasticity were calculated.The model parameters were provided for subsequent numerical analysis and the simulation results were compared.(4)The principle and method of finite element analysis are described.Based on the deletion of finite element,the numerical simulation of uniaxial tension and uniaxial compression of concrete standard specimens is carried out by using random aggregate model and element equivalent model respectively.The simulation results are compared to verify the correctness and efficiency of element equivalent model.In addition,the influences of the strength of concrete interface layer,the thickness of interface layer,the porosity of interface and the strength of mortar matrix on the overall mechanical properties of concrete specimens are also discussed.(5)The subroutine of ABAQUS is redeveloped,and the SDV7 damage variable output module program is compiled.The SDV7 variable cloud chart obtained is basically consistent with the experimental results and the results of other numerical simulation methods,and the damage variable output module has the advantages of both random aggregate model and equivalent model,realizing the development of cracks as much as possible,and at the same time improving the output efficiency of graph results.