Nonlinear Fatigue Damage Of Asphalt Concrete Under Dynamic Loading

The fatigue life prediction of asphalt concrete is mostly based on the indoor bending or indirect tensile fatigue test.However,the test has the disadvantages of long cycle,high cost and difficult popularization of technical means.Therefore,it is of practical significance to study by fatigue damage mechanics and finite element method and it can better explain the failure mechanism of asphalt pavement under repeated dynamic loading.Firstly,according to the uniaxial compression loading-deformation curves of asphalt concrete under different loading rates,the finite element model of the loading condition was established to calculate the dynamic elastic modulus of the loading moment,and the dynamic elastic modulus field equation wrote by the corresponding VUMAT subroutine was obtained with loading rate and stress state as independent variables.The method was applied to the splitting test of asphalt concrete to characterize material nonlinearity and the three point loading test of asphalt concrete to predict tensile strength.Secondly,the VUMAT subroutine of three parameter viscoelastic model was wrote,and the viscoelastic parameters were identified according to the different strain rates loading of asphalt concrete under uniaxial compression test to obtain the formula of viscoelastic parameters with strain rate.The correctness of the formula was verified by another set of data from the same experiment.Flexural and indirect tensile conditions of asphalt concrete were simulated by the VUMAT subroutine of viscoelastic parameters with strain rate and finite element software ABAQUS,and the maximum bending tensile stress amplitudes and test strengths were compared to verify applicability.Thirdly,based on the viscoelastic parameter model of strain rate,the fatigue damage models of asphalt concrete with tensile stress as an independent variable were established to predict the fatigue life of the bending and indirect tensile and compare with the traditional S-N curve prediction method.Finally,3D numerical aggregate was constructed based on two dimensional aggregate profiles and the five section method,and the geometric model of the aggregate casted was dispersed in the form of grid.According to the stress-strain curves of asphalt mortar at different strain rates,the viscoelastic parameters of strain rate were obtained.The meso fatigue damage model of asphalt mortar with first principal stress as the variable was used to evaluate the multi-point damage distributions of asphalt concrete under dynamic loading.