Application of elasto-visco-plastic constitutive model for asphalt pavement creep simulation (original) (raw)
Related papers
Computational Materials Science, 2007
ABSTRACT The study and development of recycling techniques for pavements is an increasing activity in engineering nowadays. This research line demands a more realistic characterization of the material properties with the aim of simulate the asphalt mixture’s response placed into a multilayered system over granular bases, under dynamic loads, considering also temperature variation or strength reduction for cyclic loads.In order to improve the current formulations, a new viscoplastic model has been developed assuming the strain rate dependency of the material’s response observed in the experimental tests. The strain rate variable affects in a significant way the Young modulus and the viscosity parameter of the model. According to this hypothesis a constitutive equations have been formulated. The mechanical variables involved have been calibrated according to experimental results, developing new expressions for the strain rate dependent parameters. The new viscoplastic model permits us to characterize the material’s response with a few mechanical values, easily obtained from standard laboratory tests. The results obtained show a good approximation to experimental laboratory curves for different rates of loading and temperatures.The model has been applied to simulate the response of a real flexible pavement structure conformed by two asphalt layers over two granular bases, that’s materials with different constitutive behaviors. Experimental tests in the recycled track have been made obtaining the horizontal strain evolution under dynamic load. Different loading rates and temperatures, as well as cracked and continuum pavement responses have been considered in the study. Strains were measured in the interface between the two asphalt layers and simulated using the here proposed model offering a fairly good approximation of the real response observed in the track, although the degree of variation even in the experimental curves is quite high.The results of this study represent a proper base for further developments in structural analysis of pavement layers, considering more complex phenomena, determinant in the long term material’s response, to develop a numerical tool for pavements’ design and lifetime prediction.
A thermo-viscoelastic-viscoplastic-viscodamage constitutive model for asphaltic materials
2011
A temperature-dependent viscodamage model is proposed and coupled to the temperature-dependent Schapery's nonlinear viscoelasticity and the temperature-dependent Perzyna's viscoplasticity constitutive model presented in Abu Al-Rub et al. (2009) and Huang et al. (in press) in order to model the nonlinear constitutive behavior of asphalt mixes. The thermo-viscodamage model is formulated to be a function of temperature, total effective strain, and the damage driving force which is expressed in terms of the stress invariants of the effective stress in the undamaged configuration. This expression for the damage force allows for the distinction between the influence of compression and extension loading conditions on damage nucleation and growth. A systematic procedure for obtaining the thermo-viscodamage model parameters using creep test data at different stress levels and different temperatures is presented. The recursive-iterative and radial return algorithms are used for the numerical implementation of the nonlinear viscoelasticity and viscoplasticity models, respectively, whereas the viscodamage model is implemented using the effective (undamaged) configuration concept. Numerical algorithms are implemented in the well-known finite element code Abaqus via the user material subroutine UMAT. The model is then calibrated and verified by comparing the model predictions with experimental data that include creep-recovery, creep, and uniaxial constant strain rate tests over a range of temperatures, stress levels, and strain rates. It is shown that the presented constitutive model is capable of predicting the nonlinear behavior of asphaltic mixes under different loading conditions.
Journal of Engineering Mechanics, 2007
This study presents micromechanical finite-element ͑FE͒ and discrete-element ͑DE͒ models for the prediction of viscoelastic creep stiffness of asphalt mixture. Asphalt mixture is composed of graded aggregates bound with mastic ͑asphalt mixed with fines and fine aggregates͒ and air voids. The two-dimensional ͑2D͒ microstructure of asphalt mixture was obtained by optically scanning the smoothly sawn surface of superpave gyratory compacted asphalt mixture specimens. For the FE method, the micromechanical model of asphalt mixture uses an equivalent lattice network structure whereby interparticle load transfer is simulated through an effective asphalt mastic zone. The ABAQUS FE model integrates a user material subroutine that combines continuum elements with viscoelastic properties for the effective asphalt mastic and rigid body elements for each aggregate. An incremental FE algorithm was employed in an ABAQUS user material model for the asphalt mastic to predict global viscoelastic behavior of asphalt mixture. In regard to the DE model, the outlines of aggregates were converted into polygons based on a 2D scanned mixture microstructure. The polygons were then mapped onto a sheet of uniformly sized disks, and the intrinsic and interface properties of the aggregates and mastic were assigned for the simulation. An experimental program was developed to measure the properties of sand mastic for simulation inputs. The laboratory measurements of the mixture creep stiffness were compared with FE and DE model predictions over a reduced time. The results indicated both methods were applicable for mixture creep stiffness prediction.
International Journal of Pavement Engineering, 2011
This study presents the numerical implementation and validation of a constitutive model for describing the nonlinear behaviour of asphalt mixes. This model incorporates nonlinear viscoelasticity and viscoplasticity to predict the recoverable and irrecoverable responses, respectively. The model is represented in a numerical formulation and implemented in a finite element code using a recursive -iterative algorithm for nonlinear viscoelasticity and the radial return algorithm for viscoplasticity. Then the model is used to analyse the behaviour of asphalt mixtures subjected to single creep-recovery tests at different stress levels and temperatures. This experimental analysis includes the separation of the viscoelastic and viscoplastic strain components and identification of the material parameters associated with these components. Finally, the model is applied and verified against a set of creep-recovery tests at different stress levels and temperatures.
Visco-elastic modeling for asphalt pavements–software ViscoRoute
gives a set of constitutive equations of a visco-elastic material which accounts well for the behaviour of asphalt pavement layers, especially regarding thermal effects. This model allows rather good predictions of experimental data. The French pavement design method consists in a pavement mechanistic analysis based on the Burmister multilayer elastic model (1943) -LCPC software ALIZE (1982)-. In that model, the Huet-Sayegh behaviour is taken into account with its equivalent elastic modulus at the 15°C French average temperature and a 10 Hz frequency. That frequency value is assumed to be equivalent to the standard 72 km/h French vehicle speed. Such semi-analytical calculations provide relatively good stress and strain fields for heavy traffic pavements but it is less satisfactory for flexible pavements with low traffic, for high temperature gradients and for the analysis of damages under slow heavy loads. Therefore the complete visco-elastic behaviour of each asphalt pavement layers has to be taken into account. The aim of this paper is to present a thermo-visco-elastic multi-layer model using the Huet-Sayegh behaviour. By means of the Fast Fourier transform method, the equations of the model are solved in the coordinate system of the moving load. Results are successfully compared with an analytical solution, finite element results and accelerated pavement testing data. A software called ViscoRoute (i.e. ViscoRoad) based on this modelling has been developed. The second part of this work deals with the relevance of the assumption on the time-frequency equivalence of the French design method.
Visco-elastic modelling for asphalt pavements : Software ViscoRoute
HAL (Le Centre pour la Communication Scientifique Directe), 2006
Huet-Sayegh model (1963) gives a set of constitutive equations of a visco-elastic material which accounts well for the behaviour of asphalt pavement layers, especially regarding thermal effects. This model allows rather good predictions of experimental data. The French pavement design method consists in a pavement mechanistic analysis based on the Burmister multilayer elastic model (1943)-LCPC software ALIZE (1982)-. In that model, the Huet-Sayegh behaviour is taken into account with its equivalent elastic modulus at the 15°C French average temperature and a 10 Hz frequency. That frequency value is assumed to be equivalent to the standard 72 km/h French vehicle speed. Such semi-analytical calculations provide relatively good stress and strain fields for heavy traffic pavements but it is less satisfactory for flexible pavements with low traffic, for high temperature gradients and for the analysis of damages under slow heavy loads. Therefore the complete visco-elastic behaviour of each asphalt pavement layers has to be taken into account. The aim of this paper is to present a thermo-visco-elastic multi-layer model using the Huet-Sayegh behaviour. By means of the Fast Fourier transform method, the equations of the model are solved in the coordinate system of the moving load. Results are successfully compared with an analytical solution, finite element results and accelerated pavement testing data. A software called ViscoRoute (i.e. ViscoRoad) based on this modelling has been developed. The second part of this work deals with the relevance of the assumption on the time-frequency equivalence of the French design method.
Constitutive Modeling of Asphalt-Aggregate Mixes with Damage and Healing
Research Thesis, 2006
Asphalt-aggregate mixes are being used throughout the world as a prime construction material for pavements. An asphalt mix is a multiphase heterogeneous material; it is a composite blend of air-voids, asphalt-cement (bitumen) and aggregates of a range of sizes. These materials exhibit extremely complex mechanical behavior that is very difficult to capture and model. Mainly for this reason available pavement-performance models are empirical, as no rigorous constitutive models were yet formulated for asphalt mixes. The motivation underlying this research work was to improve material modeling and characterization techniques for asphalt-aggregate mixes. An up-to-date review of literature revealed that current characterization efforts are limited principally because they deal with material behavior in uniaxial tests and provide essentially one-dimensional models. This dissertation presents the development of a triaxial viscoelastic-viscoplastic constitutive model for asphalt mixes including the effects of damage and healing. The model is confined to the description of pre-peak load response under isothermal conditions. It is based on additive separation of the total strain into viscoelastic and viscoplastic components and provides individual constitutive treatment to each part. The viscoelastic formulation is nonlinear, cross-anisotropic, and characterized by one unique (scalar) time-function. Three nonlinear isotopic effects are modeled: i) damage, i.e. loss of stiffness under load; ii) stiffening, i.e. increase of stiffness under compression conditions, and iii) healing, i.e., a decrease in the level of damage during rest periods. The viscoplastic equations resemble the kinematic-hardening formulations used to describe creep of metals. Internal stress-like variables are used to produce hardening (or softening) in each direction. Neither damage nor healing is included in the viscoplastic model. It should be noted that coupling is introduced between the individual formulations, making the viscoelastic response dependent also on the viscoplastic component. In order to support the development of the constitutive formulation, new experimental procedures were designed and executed using the triaxial apparatus. Creep and recovery test results are presented and analyzed, providing means (also) to calibrate and validate the model for biaxial stress-conditions and one test temperature. Good reproducibility and forecast-ability were obtained in the analyses of versatile test-data for both small and large strain load-cycles; indicating that the model is suitable for simulating the 3D load-response of asphalt-aggregate mixes. The constitutive development in this study constitutes the first attempt to describe the triaxial (viscoelastic-viscoplastic) load-response of asphalt materials including damage and healing. Several aspects of this development were found limited - specifically the ability to rigorously describe the viscoplastic behavior after large rest periods. Further research is needed to try and resolve this limitation and remove some of the other formulation restrictions.
International Journal for Numerical and Analytical Methods in Geomechanics, 2012
Based on the continuum damage mechanics, a general and comprehensive thermodynamic-based framework for coupling the temperature-dependent viscoelastic, viscoplastic, and viscodamage behaviors of bituminous materials is presented. This general framework derives systematically Schapery-type nonlinear viscoelasticity, Perzyna-type viscoplasticity, and a viscodamage model analogous to the Perzyna-type viscoplasticity. The resulting constitutive equations are implemented in the well-known finite element code Abaqus via the user material subroutine UMAT. A systematic procedure for identifying the model parameters is discussed. Finally, the model is validated by comparing the model predictions with a comprehensive set of experimental data on hot mix asphalt that include creep-recovery, creep, uniaxial constant strain rate, and repeated creep-recovery tests in both tension and compression over a range of temperatures, stress levels, and strain rates. Comparisons between model predictions and experimental measurements show that the presented constitutive model is capable of predicting the nonlinear behavior of asphaltic mixes under different loading conditions. In terms of the viscoelastic behavior of materials, Biot [13] derived a formulation for linear viscoelastic materials. Schapery used the thermodynamics of irreversible processes and developed a single integral constitutive model for nonlinear viscoelastic materials such as polymers . Schapery's constitutive model has been applied to asphalt mixes by several researchers (e.g. ). Later, Touti and Cederbaum [22], Haj-Ali and Muliana [16], and Huang et al. [18] developed algorithms for numerical implementation of Schapery's viscoelastic constitutive model in finite element codes. Recently, Levesque et al. [12] extended Schapery's nonlinear viscoelastic model for 3D applications based on laws of thermodynamics. In terms of the viscoplastic behavior of asphalt mixes, Perzyna's theory [23] has been used by several researchers for predicting the permanent deformation in asphalt mixes. For example, Lu and Wright [24] and Masad et al. [25] used Perzyna's viscoplasticity for modeling mechanical response of hot mix asphalt (HMA). Saadeh et al. [26], Huang [27], and Abu Al-Rub et al. [20] coupled Schapery's nonlinear viscoelasticity model to Perzyna's viscoplasticity model to more accurately simulate the nonlinear mechanical response of HMA at high stress levels and high temperatures.