Development and numerical implementation of nonlinear viscoelastic-viscoplastic model for asphalt materials

摘要

Hot mix asphalt (HMA) is a composite material which consists of aggregates, airvoids and asphalt materials. The HMA response is typically described to beviscoelastic-viscoplastic, and its response is a function of temperature, stress/strain rate,and stress/strain level. Many researches have shown that the viscoelastic response ofasphalt mixtures can be nonlinear once the stress/strain value exceeds a certain thresholdlevel. This study presents a nonlinear viscoelastic-viscoplastic model for describing thebehavior of asphalt materials under various conditions. A new method is developed inthis study for separating the viscoelastic response from the viscoplastic response.The first part of this study focuses on the implementation of Schapery nonlinearviscoelastic model in finite element (FE) using a user-defined material subroutine(UMAT) within the ABAQUS commercial software. The FE implementation employsthe recursive-iterative integration algorithm, which can improve the convergence andsave the calculating time. The verification of the nonlinear viscoelastic model isachieved by analyzing (1) the response of asphalt mixtures tested in the Simple Shear Test (SST) at several temperatures and stress levels, (2) the response of unaged and agedasphalt binders tested in the Dynamic Shear Rheometer (DSR), and (3) the response ofasphalt binders in the multiple stress creep recovery test (MSCR).In the second part of this study, the nonlinear viscoelastic-viscoplasticconstitutive relationship is implemented using UMAT. The viscoplastic component ofthe model employs Perzyna?s theory with Extended Drucker-Prager yield surface whichis modified to account for the difference in material response under compression andextension stress states. The study includes parametric analysis to illustrate the effect ofnonlinear viscoelastic parameters and viscoplastic parameters on the asphalt mixresponse. The capability of the model in describing the fatigue and permanentdeformation distresses of asphalt pavements is illustrated using finite elementsimulations.The constitutive model developed in this study can describe the behavior ofasphalt materials (asphalt binder, asphalt mastic and mixtures) under various testingconditions. This study also achieved the FE implementation of a nonlinear viscoelasticviscoplasticconstitutive model that can simulate the fatigue and permanent deformationdistresses of asphalt pavement structures.