| Concrete material is a heterogeneous multi-phase medium.When the structure is not in service,it contains a large number of randomly distributed voids,micro-cracks and other initial damage.Primary pore and crack will weaken the mechanical properties of concrete materials,and will continue to expand and evolve under the change of external environment,which will eventually lead to structural damage and loss of bearing capacity,so the failure form can only represent its stress history and failure form to a limited extent.Therefore,in order to describe the evolution process of crack propagation and its failure mechanism of concrete structures,it is necessary to study the influence of randomness and non-linearity from the point of view of damage mechanics,and explore its evolution mechanism and failure basis.In this paper,EPS particles are used to simulate the initial voids in concrete materials.Starting from concrete materials with different initial voids,the effects of initial voids on the basic mechanical properties of concrete materials and the law of crack propagation are discussed.A damage constitutive model considering initial voids is established,and finite element analysis software is used to simulate crack propagation path of reinforced concrete beams without initial defects.The main research contents are as follows:(1)The basic mechanical properties of concrete specimens with initial porosity are tested.The strength,modulus of elasticity and stress-strain curves of concrete specimens with initial porosity of 0%,2%,4% and 6% are measured by cubic compression,prism compression and cubic splitting tension tests.The influence of initial porosity change on basic mechanical parameters is analyzed,and the formula between basic mechanical parameters and initial porosity is established by regression analysis.(2)Through the four-point bending test of reinforced concrete beams with initial voids,the failure process,failure mode and bearing capacity of the beams areexplored.Based on the fractal theory,the randomness and irregularity of crack propagation on the surface of beams are explored,and the evolution of crack propagation is quantitatively described.The relationship between the fractal dimension of crack propagation path and mechanical parameters is established to judge the damage degree of reinforced concrete members under load.(3)Based on the complete stress-strain curve obtained from uniaxial compression test of concrete with initial porosity and the fractal dimension of surface cracks of reinforced concrete beams obtained from four-point bending test,a fractal damage constitutive model is established by means of Weibull statistical method and damage mechanics theory,and the damage evolution law is quantitatively explored.The damage is established based on the fractal dimension of surface cracks of test beams.The constitutive model is used to calculate the flexural capacity of the test beam.(4)By using the finite element analysis software and the extended finite element method in numerical simulation,the whole cracking process of the test beam without prefabricated voids and the same specification as the physical test is simulated,and the crack propagation evolution process is obtained.Through numerical simulation,the evolution process of crack distribution and its non-linear characteristics,mechanism and law in the process of concrete loading and failure are revealed step by step,and verified with the physical test results,which proves the operability of the extended finite element numerical simulation method. |
