The Study Of Fatigue Damage On Asphalt Pavement Based On Viscoelastic Damage Model

Asphalt mixture has been widely used in pavement engineering.Its fatigue phenomenon due to the repeated vehicle load is generally considered to be one of the major failure factors in asphalt pavement structures.A series of empirical results on fatigue damage of asphalt mixture have been obtained through experimental research,but these results turn out to be different from the pavement performance in practical engineering,and the internal damage mechanism is still unclear.At present,few studies have been carried out on the numerical simulation of asphalt fatigue performance.In this case,the present paper proposes a mechanical method which achieves fatigue damage analysis of asphalt mixture from modeling to computation.This method adopts a new type of viscoelastic constitutive model coupled with damage,includs the fatigue test evaluation framework,and the corresponding numerical simulation is realized in the commercial software ABAQUS through secondary development.The main work is summarized as follows:1.A new type of viscoelastic constitutive model coupled with damage is proposed based on damage theory and viscoelastic theory.The classical damage theory is used to describe the fatigue damage behavior of asphalt mixtures through deep study of thermodynamics.At the same time,the classical and fractional viscoelastic constitutive models are used to describe the stress-strain relationship of asphalt respectively.According to the comparisons with the experimental results in laboratory,the fractional viscoelastic model can more accurately reveal the mechanical properties of asphalt mixtures.After that,the viscoelastic model coupled with damage is established,which is taken as the theoretical model in the present method.2.The numerical incremental scheme of the constitutive model coupled with damage was derived and then realized in the material custom subroutine UMAT(User-defined Material)of ABAQUS.For classical viscoelastic constitutive model,the characteristics of exponential function and Prony series function are considered in derivation.For fractional viscoelastic model which is more complex,the Prony series function is used to approximate the theoretical model and then a new parameter is introduced to extend the application of this approximation.And then,the numerical incremental scheme is derived by the full coupling method.3.The damage evolution of asphalt mixtures is investigated based on the results in laboratory testing,the analysis framework for fatigue tests is proposed,and a series of material parameters are obtained which are required by numerical implementation of the theoretical model.The damage evolution has shown a three-stage development trend.Using energy ratio parameters and damage evolution models,the macroscopic crack development and material damage prediction formulae are obtained.Through the theoretical computation,an equivalent calculation method of cyclic load is obtained.Finally,a fatigue life prediction model based on stress level and dynamic modulus is obtained,which considers the influence of load level and the rest time at the meantime.4.The FE(finite element)models on the scale of specimen and pavement are constructed and computed in Abaqus respectively,the results of which verify the feasibility and efficiency of the proposed method.Firstly,the FE model of fatigue test specimen is established and then the results from ABAQUS are compared with those from tests.At the same time,the influence of the load amplitude and rest time on the damage evolution is analyzed.Secondly,a two-dimensional pavement model is established,the numerical results are analyzed,and the damage development of pavement considering the load level and driving speed parameters are studied.