| Concrete material is a kind of heterogeneous,isotropic,and with the change of time and environmental conditions of multiphase mixed materials,which has a large number of original defects such as randomly distributed pores and micro cracks and so on.The existence of these defects will weaken the mechanical properties of concrete material.It expands and evolves under the change of external environment,which will eventually lead to the destruction of building structure and the loss of bearing capacity,and the destruction form can only represent its destruction form to a limited extent.So far,almost all mechanical theories have been used to establish the constitutive model of concrete,but none of them is recognized to be able to completely describe the constitutive behavior of concrete.Therefore,to accurately describe the concrete structure crack extension evolution process and damage mechanism,we must from the perspective of damage mechanics,explore its evolution mechanism and failure of the basis,to explore a scientific and reasonable concrete constitutive model for finite element simulation,it can not only improve the level of construction of the construction industry has the positive significance but also a very important fundamental frontier.The contents are as follows:(1)Considering the applicability and flexibility of the constitutive model contained in the ABAQUS finite element software material library,based on the statistical damage theory,the orthotropic statistical damage model of concrete established by Bai Weifeng et al is taken as the basis.In this model,uniaxial tension and compression are considered as the basic macro failure modes,and fracture and yield are considered as the two micro damage mechanisms.Among them,the evolution process of meso-damage shows obvious regularity,which can be represented by the change law of the five characteristic parameters in the statistical damage model.Based on FORTRAN language,using VUMAT user subroutine interface,the written subroutine is embedded into the main program of ABAQUS to realize the secondary development.The single element model is used to predict the uniaxial tensile and compression process of concrete test blocks,and the rationality of the model is verified.(2)The basic mechanical properties of concrete blocks with different freeze-thaw damage times and different silica powder contents were tested.Through design tests,uniaxial compression and split tensile tests were carried out on concrete blocks with freeze-thaw times of 0,25,50,75,100,125,150 and silica powder contents of 0%,3%,6%,9% and 12%respectively,and their elastic modulus and strength were measured.Thus,uniaxial compression stress-strain curves under different freeze-thaw damage and silica powder contents were obtained.The effects of freeze-thaw damage and silica powder change on the basic mechanical properties and parameters of concrete are analyzed.(3)The finite element software ABAQUS is used to carry out numerical analysis of the three-point bending beam,and the numerical simulation of the three-point concrete beam under different crack height ratios a =0,0.2,0.4 and 0.6 is carried out.The ultimate deformation,failure mechanism and maximum bearing capacity of the three-point concrete beam in the process of stress are discussed.Based on the experimental data,the damage model parameters considering the effects of freeze-thaw damage and silica powder content were obtained.Further,the numerical simulation of the three-point bending beam considering the effects of freeze-thaw damage and silica powder content was carried out,and the required meso-damage parameters were obtained from the corresponding test data.Then,the whole process of the concrete beam from loading to failure is simulated by prefabricating different initial cracks.The effects of freeze-thaw damage and silica powder content on the bearing capacity and crack propagation process of the three-point bending beam are analyzed.The validity,feasibility and applicability of the model are verified. |
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