UCLA

New initial strain energy based thermo-elastoviscoplastic isotropic and two-parameter damage-self healing formulations for bituminous materials are proposed and employed for comparisons between model predictions and experimental measurements. First, a class of elastoviscoplastic constitutive isotropic damage-self healing model, based on a continuum thermodynamic framework, is developed within an initial elastic strain energy based formulation. An Arrhenius-type temperature term is proposed and uncoupled with Helmholtz free energy potential to account for the effect of temperature. In particular, the governing incremental damage and healing evolutions are coupled and characterized through the net stress concept in conjunction with the hypothesis of strain equivalence. The viscoplastic flow is introduced by means of an additive split of the stress tensor. The (undamaged) energy norm of strain tensor is redefined as equivalent strain and employed for damage and healing criteria. A rate-dependent (viscous) damage model with a structure analogous to viscoplasticity of the Perzyna type is used for rate sensitivity of bituminous materials.

Computational algorithms based on the two-step operator splitting methodology are systematically proposed and implemented for numerical simulations. The elastic damage self-healing predictor and the viscoplastic corrector coupled with Arrhenius-type temperature term via the net stress concept in conjunction with the hypothesis of strain equivalence are considered as numerical implementation of the models. Experimental validation of the proposed formulations against monotonic constant-strain test under different temperatures and controlled-strain cyclic tension test is presented. Qualitative and quantitative agreement between experimental results and numerical simulations is observed. In particular, the softening behavior of the bituminous materials is well predicted for monotonic constant-strain rate-test and the viscous damage behavior can be reasonably captured by the proposed new damage models with the Arrhenius-type temperature term and step-by-step computational algorithms.

Secondly, new initial strain energy based thermo-elastoviscoplastic two-parameter damage-self healing formulations for bituminous composites are developed and employed for comparisons between computational simulations and experimental data. In general, the fourth-order form of isotropic damage tensor is composed of two independent parts: the volumetric and deviatoric parts. If the damage in volumetric part has the same magnitude as deviatoric part, the damage tensor can lead to a scalar damage model which implies that the Poisson's ratio remains constant when degradation continues pointed out by Ju (1990). A class of elastoviscoplastic two-parameter constitutive damage-self healing model, based on a continuum thermodynamic framework, is proposed within an initial elastic strain energy based formulation. Helmholtz free energy potential is employed and uncoupled with an Arrhenius-type temperature term in order to account for the effect of temperature. In particular, the governing incremental damage and healing evolutions are coupled in volumetric and deviatoric parts and characterized through the net stress concept in conjunction with the hypothesis of strain equivalence. The (undamaged) energy norm of volumetric and deviatoric strain tensors as equivalent volumetric and deviatoric strain is redefined and used for two-parameter damage and healing criteria. A rate-dependent (viscous) volumetric and deviatoric damage model with a structure analogous to viscoplasticity of the Perzyna type is used for rate sensitivity of bituminous composites. Completely new computational algorithms are systematically developed based on the two-step operator splitting methodology. It is observed that numerical simulations by two-parameter model agree well with experimental results. In particular, the softening responses of the bituminous composites is well predicted for monotonic constant-strain rate test and the viscous damage behavior can be reasonably predicted by the proposed two-parameter damage models with the Arrhenius-type temperature term and step-by-step computational algorithms. It is noted that the two-parameter model can better predict the thermo-mechanical behavior of asphalt and is more versatile than the isotropic damage-self healing model.