Studies On Fatigue Damage Constitutive Model And Evaluation Method Of Fatigue Performance Of Concrete

In civil engineering,concrete is the most widely used material,study on its various performance is important obviously.Because of its complex composition and certain randomness,its mechanical properties also showed a certain degree of random and nonlinear.Therefore the study of mechanical properties of concrete are also has certain difficulties.Constitutive model of concrete is one of the most important problems in concrete research.It has always been focus of concrete research at domestic and overseas.In the past concrete calculation,people often pay more attention to its bearing capacity checking,but neglect the degradation of mechanical performance of concrete structure under fatigue loading.In fact,the fatigue load has a great influence on the life of concrete structure.So it is very important to study the fatigue performance of concrete.This paper has carried out the following effective research content in view of this problem.(1)In this paper,with the mesoscopic physics mechanism in the process of concrete fatigue damage evolution,based on a lower scale fracture model,the development of micro holes and crack is transformed into fracture damage of microstructure in the model.Through the research on fatigue of the material energy dissipation in the evolution process,using the damage mechanics under the frame of irreversible thermodynamics,this paper proposes equation of fatigue damage consistent with the actual situation.A fatigue constitutive relation model with simple form and accuracy rate.On this basis,the obtained constitutive model is written into a FORTRAN program,and the proposed constitutive model is applied to numerical calculation through the ABAQUS/UMAT interface,which makes the constitutive model have practical value.By ABAQUS/UMAT interface,the proposed constitutive model was applied to numerical calculation.(2)Because of two time scales of loading cycle and fatigue life in the fatigue problem,there is a huge difference between the two time scales.Therefore,it takes a long time to calculate the fatigue simulation.In order to solve this problem,based on the principle of trend extrapolation,an accelerating algorithm of fatigue finite element calculation is proposed.Based on applying external program to control the finite element software ABAQUS,the appropriate jump step length was selected in order to jump some calculate cycles,so that time of jumping step was saved.This method improve the efficiency of the fatigue damage calculation with the guarantee of accuracy of the fatigue calculation.The accelerating algorithm made the constitutive model could be applied to solve practical problems.In this paper,a concrete element is selected to verify the acceleration algorithm.The results show that the accelerated calculation performance good accuracy and the fatigue calculation time was saved effectively.(3)Finally,this paper selected the fatigue test model of concrete notched beam and reinforced concrete beam,applies the constitutive model and numerical acceleration algorithm proposed in this paper,analyze the fatigue damage performance of the structure.The results show that the conclusions of this paper can describe and predict the fatigue performance of concrete well,and have certain guiding significance for fatigue damage analysis in engineering practice.