Study On Three-dimensional Viscoelastic Constitutive Model And Mechanical Behavior Test Of Asphalt Mastic

Asphalt pavement has become the main pavement of high-grade roads in China,and asphalt mixture is the main material of asphalt pavement.Constitutive relationship is one of the most basic mechanical relations,and its correctness determines the accuracy of load and response description.According to the modern mortar theory,asphalt mastic is composed of asphalt,filler and fine aggregate,and asphalt mixture is composed of coarse aggregate.Asphalt mastic has the characteristics of viscoelastic material.Studying its constitutive relationship is one of the bases of a series of studies on asphalt pavement.It can provide ideas,methods and tools for the follow-up study of asphalt mixture.The traditional research on the constitutive relationship of asphalt mastic is mostly confined to one-dimensional viscoelastic constitutive model,the main means are uniaxial test and corresponding numerical simulation,which is far from the real three-dimensional situation.At present,some achievements have been made in the study of three-dimensional viscoelastic constitutive model of asphalt mastic,but it is still in the stage of exploration and development.Therefore,based on the classical viscoelastic constitutive model in the basic viscoelastic theory,this paper establishes a three-dimensional viscoelastic constitutive model and realizes it by numerical simulation.Study on mechanical behavior test and corresponding numerical simulation of asphalt mastic.The main contents are as follows:(1)A three-dimensional viscoelastic constitutive model based on Burgers model,four-element five-parameter model and generalized model is established.Based on the assumptions of isotropy,homogeneity and small deformation,considering the viscoelasticity of spherical tensor and partial tensor,the Burgers model,four-element five-parameter model and generalized model in onedimensional case are extended in three dimensions.The material functions and integral expressions of each model in three-dimensional case are obtained.Burgers model and generalized model are divided into creep and relaxation models.The results show that the three-dimensional viscoelastic constitutive model can predict the three-dimensional load response well within the allowable error range.(2)The three-dimensional viscoelastic constitutive model based on Burgers model,four-element five-parameter model and generalized model is numerically realized.Based on Abaqus calculation rule and UMAT(user subroutine to define a material’s mechanical behavior),the three-dimensional viscoelastic constitutive model is discretized by using Schapery’s non-linear three-dimensional viscoelastic material model finite element method proposed by Haj-Ali.The program is developed in Fortran language and imported into Abaqus to realize transportation successfully.The results shows that the Abaqus user subroutine UMAT is feasible and correct.(3)The uniaxial compression test,local triaxial compression test and corresponding numerical simulation of asphalt mastic under multi-displacement load were compared.Uniaxial compression test and local triaxial test of asphalt mastic under different displacement loads were carried out using MTS809 electrohydraulic servo tension-torsion material testing machine.Abaqus finite element numerical simulation of corresponding test was carried out based on material function parameters measured by uniaxial creep test and user subroutine UMAT.The results show that the three-dimensional viscoelastic constitutive model based on Burgers model is more suitable for practical application,with high accuracy,fewer parameters and high efficiency.The three-dimensional viscoelastic constitutive model based on four-element and five-parameter model is more suitable for application under three-dimensional stress loading.