UCLA

Innovative micromechanical-based isotropic formulations have been proposed to predict the mechanical behavior of the asphalt concrete materials featuring high toughness, low viscosity nano-molecular resins and employed for comparisons between model predications and experimental measurements. A class of isotropic elastic-damage model based on a continuum thermodynamic framework is developed within an initial elastic strain energy based formulation. A 3-D analytical modeling methodology is established by treating the revolutionary asphalt concrete material as an asphalt mastic composite matrix containing fine aggregates, asphalt binder, polymerized DCPD and air voids with coarse aggregates inhomogeneities distributed in it . The effective elastic moduli of the asphalt mastic composites are homogenized by a newly proposed multilevel homogenization approach based on an ensemble-volume averaged pairwise interacting theory. The coarse aggregates are represented by spherical multilayer-coated particles in certain sizes. A governing damage evolution criterion is characterized through the net stress concept in conjunction with the hypothesis of strain equivalence.

An analytical formulation to predict the isotropic viscoelastic properties of the multiphase asphalt mastic composites is proposed within the micromechanical framework based on the concept of the correspondence principle along with the Laplace transform. The viscous behavior induced by the asphalt binder phase is characterized by a 4-parameter Burgers model, from where a multilevel homogenization approach similar to the elastic framework is employed to evaluate the effective viscoelastic mechanical properties of the heterogeneous asphalt mastic composites.

A class of isotropic elastoplastic-damage framework and isotropic thermo-elasto- viscoplastic-damage framework are developed following a similar methodology of the isotropic elastic-damage framework. The plastic and viscoplastic flows are introduced by means of an additive split of the stress tensor and the energy norm of strain tensor is redefined and employed as the equivalent strain. In particular, the Drucker-Prager yield condition is employed to characterize the plasticity behavior and a linear Perzyna type associative flow rule and viscoplastic hardening law are characterized in terms of the effective quantities in the effective stress space. A rate-dependent damage evolution criterion is introduced within the initial elastic strain energy based micromechanical framework to implement the damage behavior. An Arrhenius-type temperature term, uncoupled with Helmholtz free energy potential, is introduced to account for the effect of temperature. The computation of coupled elastoplastic/ elasto-viscoplastic damage behaviors are realized by a two-step operator splitting methodology.

Numerical simulations are conducted based on the proposed formulations. Particularly, the 3-D modeling is achieved by Python scripting in ABAQUS to make sure there is no overlapping among spherical particle inclusions; while the two-step operator splitting computational algorithms are accomplished through Fortran UMAT. Prediction results are compared with suitably designed experimental data, showing reasonably good agreement.