Permanent Deformation Calculation Based On The Complex Tire-pavement Contact Stress

Rutting(permanent deformation)is a common early age distress of asphalt pavement.Different from most of the previous studies where the tire-pavement contact stress is simplified extensively,this dissertation is aimed at demonstrating the influence of the real complex tire-pavement contact stress on the permanent deformation of asphalt pavement.Firstly,a tire-pavement contact FEM(finite element method)model was built to calculate the stress distribution on the tire-pavement interface.Then the stress distribution was applied to a viscoelastic FEM pavement model as a moving load to calculate the permanent deformation.This method was then used to evaluate the influence of tire rolling condition on the tire-pavement stress distribution.In the tire-pavement contact model,a mixed Lagrangian/Eulerian method was used to simulate the rolling contact problem of tire under different rolling conditions.Results shows that the tire load,the inflation pressure,the friction coefficient,the torque on the tire axle and the slip angle have a great influence on the tire-pavement contact distribution.The viscoelasticity coefficients of asphalt pavement FEM model were obtained by conducting dynamic creep tests.The deformation formula under the havesine loading in the dynamic creep test was deduced by linear superposition principle.Then,the Prony series viscoelasticity coefficients were fitted by nonlinear fitting software Origin,and the deduce deformation formula acted as the nonlinear function in the nonlinear fitting.After that,the validity of the coefficients were verified by a FEM model of the dynamic creep test.In the FEM pavement model which used to calculate the permanent deformation,the quasi-static analysis and implicit dynamic analysis method were compared,the effect of the velocity was also studied.Result shows that these two methods has their own range of application.The implicit dynamic analysis is more suitable for analysis the transient response of the pavement(such as the transient deformation),while the quasi-static analysis is more suitable for long-term response(such as permanent deformation).In addition,the computation cost of quasi-static analysis is much smaller than implicit dynamic analysis.Therefore,the quasi-static analysis is more suitable for calculating the permanent deformation of asphalt pavement.Finally,by the permanent deformation calculation method introduced above,the influence of velocity of tire,the temperature of pavement,the tire load,the inflation pressure,the friction coefficient the torque on the tire axis and the slip angle on the permanent deformation were studied.Result shows that,the permanent deformation also grows with the tire load.While tire inflation pressure has little influence on the vertical permanent deformation,the horizontal permanent deformation decrease with it.The friction coefficients of road surface have a great effect on the horizontal permanent deformation but little effect on the vertical permanent deformation.The horizontal deformation caused by the horizontal tire-pavement contact stress under braking,traction or cornering condition can be larger than the vertical permanent deformation in some extreme cases.Therefore,the horizontal stress and permanent deformation cannot be ignored in pavement mechanical analysis.The permanent deformation is very sensitive to the variation of temperature and tire moving speed.The permanent deformation grows rapidly with the raising of temperature,while decrease exponentially with tire moving speed.The permanent deformation under high temperature(or low speed)is much greater than those in medium or low temperature(or high speed).Therefore,in order to raise the accuracy of permanent deformation prediction.The complex contact stress distribution in tire-pavement interface should be considered in pavement mechanical analysis.