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Development of Energy-based Damage and Plasticity Models for Asphalt Concrete Mixtures
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.ORCID iD: 0000-0003-2849-5263
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Characterizing the full range of damage and plastic behaviour of asphalt mixtures under varying strain-rates and stress states is a complex and challenging task. One reason for this  is partly due to the strain rate and temperature dependent nature of the material as well as the variation in the properties of the constituent materials that make up the composite asphalt mixture. Existing stress-based models for asphalt concrete materials are developed based on mechanics principles, but these models are, however, limited in their application for actual pavement analysis and design since rate dependency parameters are needed in the constitutive model to account for the influence of the strain rate on the stress-based yield and evolution criteria. Till date, we are yet to arrive at simple and comprehensive constitutive models that can be used to model the behaviour of asphalt mixture over a wide range of strain-rate which is experienced in the actual pavement sections. The aim of this thesis is to develop an increased understanding of the strength and deformation mechanism of asphalt mixtures through multi-scale modeling and to develop simple and comprehensive continuum models to characterize the non-linear behaviour of the material under varying stress-states and conditions. An analysis framework is developed for the evaluation of the influence of asphalt mixture morphology on its mechanical properties and response using X-Ray CT and digital image processing techniques. The procedure developed in the analysis framework is then used to investigate the existence of an invariant critical energy threshold for meso-crack initiation which serves as the basis for the development of a theory for the development of energy-based damage and plastic deformation models for asphalt mixtures. A new energy-based viscoelastic damage model is developed and proposed based on continuum damage mechanics (CDM) and the thermodynamics of irreversible processes. A second order damage variable tensor is introduced to account for the distributed damage in the material in the different principal damage directions. In this way, the material response in tension and compression can be decoupled and the effects of both tension- and compression stress states on the material behaviour can be accounted for adequately. Based on the finding from the energy-based damage model, an equivalent micro-crack stress approach is developed and proposed for the damage and fracture characterization of asphalt mixtures. The effective micro-crack stress approach takes account of the material stiffness and a critical energy threshold for micro-crack initiation in the characterization of damage and fracture properties of the mixture. The effective micro-crack stress approach is developed based on fundamental mechanics principles and it reduces to the Griffith's energy balance criterion when purely elastic materials are considered without the need for the consideration of the surface energy and a crack size in the determination of the fracture stress. A new Continuum Plasticity Mechanics (CPM) model is developed within the framework of thermodynamics to describe the plastic behaviour of asphalt concrete material with energy-based criteria derived for the initiation and evolution of plastic deformation. An internal state variable termed the "plasticity variable" is introduced to described the distributed dislocation movement in the microstructure. The CPM model unifies aspects of existing elasto-plastic and visco-plastic theories in one theory and shows particular strength in the modeling of rate-dependent plastic behaviour of materials without the need for the consideration of rate dependency parameters in the constitutive relationships. The CPM model is further extended to consider the reduction in the stiffness properties with incremental loading and to develop a unified energy-based damage and plasticity model. The models are implemented in a Finite Element (FE) analysis program for the validation of the models. The result shows that the energy-based damage and plastic deformation models are capable of predicting the behaviour of asphalt concrete mixtures under varying stress-states and strain-rate conditions. The work in this thesis provides the basis for the development of more fundamental understanding of the asphalt concrete material response and the application of sound and solid mechanics principles in the analysis and design of pavement structures.

Abstract [sv]

En heltäckande karakterisering av skador och plastiska beteende hos asfaltblandningar under varierande belastningshastighet och spänningstillstånd är en komplex och svår uppgift. En orsak till detta är relaterat till materialets belastningshastighet- och temperaturberoende, såväl som variationen i materialegenskaperna hos de ingående komponenterna i den sammansatta asfaltblandningen. Befintliga spänningsbaserade modeller för asfaltbetongmaterial är utvecklade baserade på mekanikprinciper, men dessa modeller är begränsade när det gäller analys och design av verkliga asfaltsbeläggningar eftersom hastighetsberoende parametrar behövs i den konstitutiva modellen även med hänsyn till töjningshastighetens inverkan på kriterier för gränser och utveckling av spänningstillstånd. Det finns därför behov av att utveckla enkla men ändå heltäckande konstitutiva modeller som kan användas för att modellera beteendet hos asfaltmassan över ett brett spektrum av belastningshastigheter för olika av sektioner asfaltsbeläggningar. Syftet med denna avhandling är att öka förståelsen av hållfasthets- och deformationsmekanismer för asfaltblandningar genom multi-modellering. Målet är att utveckla enkla och heltäckande kontinuummodeller som karakteriserar materialets olinjära beteende under varierande spänningstillstånd och betingelser. Ett analysramverk har utvecklats för utvärdering av påverkan av asfaltmassans morfologi på dess mekaniska egenskaper och beteende med hjälp av röntgendatortomografi och digital bildbehandlingsteknik. Detta förfarande har sedan använts för att undersöka förekomsten av inneboende kritiska tröskelvärden för brottenergin för mesosprickinitiering vilket i sin tur ligger till grund för utvecklingen av en teori för modellering av energibaserade skador och plastisk deformation hos asfaltblandningar. En ny energidensitet baserad viskoelastisk skademodell utvecklas och föreslås utgå från kontinuum-skade-mekanik (CDM) och termodynamik för irreversibla processer. En andra ordningens skadevariabeltensor införs för att ta hänsyn till  skadedistributionen i materialen i de olika principiella skaderiktningarna. På detta sätt kan materialets respons i drag- och tryckbelastning separeras och effekterna av spänningstillstånd i både drag och tryck kan beaktas på ett adekvat sätt. Baserat på resultaten från den energibaserade skademodellen utvecklas och föreslås en motsvarande metod för mikrosprickspänning gällande skade- och brottkarakteriseringen av asfaltblandningar. Metoden för den effektiva mikrosprickspänningen tar hänsyn till materialets styvhet och en kritisk tröskelenergi för mikrosprickinitiering för karakteriseringen av skador och brottegenskaper hos blandningen. Denna metod är utvecklad baserat på grundläggande mekanikprinciper och kan för rent elastiska material reduceras till Griffiths energibalanskriterium utan hänsyn till ytenergi och sprickstorlek vid bestämningen av brottspänningen. En ny termodynamikbaserad modell för kontinuumplasticitetsmekanik (CPM) utvecklas för att beskriva det plastiska beteendet hos asfaltbetongmaterial med energibaserade kriterier härledda för initiering och progression av plastisk deformation. En intern tillståndsvariabel kallad "plasticitetvariabeln" införs för att beskriva den fördelade dislokationsrörelsen i mikrostrukturen. CPM-modellen förenar befintliga elasto-plastiska och visko-plastiska teorier i en teori och visar sig vara särskilt effektiv i modelleringen av hastighetsberoende plastiskt beteende hos material utan att behöva beakta hastighetsberoende parametrar i de konstitutiva sambanden. CPM-modellen utvidgas ytterligare för att kunna beakta reduktionen av styvheten med stegvis ökad belastning och för att utveckla en enhetlig energibaserad skade- och plasticitetmodell. Modellerna är implementerade i ett finit element (FE)-analysprogram för validering av modellerna. Resultatet visar att de energibaserade modellerna för skador och plastisk deformation kan förutsäga beteendet hos asfaltbetongblandningar under varierande spänningstillstånd och töjningshastighetsförhållanden. Arbetet i denna avhandling utgör grunden för utvecklingen av mer grundläggande förståelse av asfaltbetongmaterialets respons och tillämpningen av sunda och robusta mekanikprinciper i analys och design av asfaltstrukturer.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. , p. 88
Series
TRITA-BYMA, ISSN 0349-5752 ; 2017:01
Keyword [en]
energy-based models, damage, X-ray computed tomography, continuum plasticity mechanics CPM, effective micro-crack stress
National Category
Civil Engineering
Research subject
Transport Science
Identifiers
URN: urn:nbn:se:kth:diva-198663ISBN: 978-91-7729-242-5 (print)OAI: oai:DiVA.org:kth-198663DiVA, id: diva2:1057977
Public defence
2017-01-27, V2, Teknikringen 76, Stockholm, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Transport Administration
Note

QC 20161220

Available from: 2016-12-20 Created: 2016-12-19 Last updated: 2016-12-20Bibliographically approved
List of papers
1. Mechanics-based Topdown Fatigue Cracking Initiation Prediction Framework for Asphaltic Pavements
Open this publication in new window or tab >>Mechanics-based Topdown Fatigue Cracking Initiation Prediction Framework for Asphaltic Pavements
2015 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 4Article in journal (Refereed) Published
Abstract [en]

In this paper, a new mechanics-based top-down fatigue cracking analysis framework is presented for asphalt pavements. A new mixture morphology-based set of material sub-models is presented for characterising key mixture properties and their change over time. Predicting the load induced top-down fatigue crack initiation (CI) time by utilising comprehensive mixture properties creates the possibility of optimising the mixture morphology while taking into account its subsequent effect on long-term pavement performance. The new framework was calibrated and subsequently validated against a number of field pavement sections with varying traffic levels that are representative for current practices and which have a wide range in material properties. The framework accounts the change in key mixture properties due to ageing and mixture-healing effect on damage accumulation while determining the overall effect of design inputs on cracking performance. Model calibration and validation were achieved based on the healing potential of the asphalt mixture. It was found out that the CI predictions for all the sections are in general agreement with the observed performance in the field, thus giving credibility for the framework.

Place, publisher, year, edition, pages
Taylor & Francis, 2015
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-164887 (URN)10.1080/14680629.2015.1055335 (DOI)
Note

QC 20161220

Available from: 2015-04-20 Created: 2015-04-20 Last updated: 2017-12-04Bibliographically approved
2. Towards Asphalt Mixture Morphology Evaluation with the Virtual Specimen Approach
Open this publication in new window or tab >>Towards Asphalt Mixture Morphology Evaluation with the Virtual Specimen Approach
2015 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed) Published
Abstract [en]

The morphology of asphalt mixture can be defined as a set of parameters describing the geo-metrical characteristics of its constituent materials, their relative proportions as well as spatialarrangement in the mixture. The present study is carried out to investigate the effect of themorphology on its meso- and macro-mechanical response. An analysis approach is used forthe meso-structural characterisation based on the X-ray computed tomography (CT) data.Image processing techniques are used to systematically vary the internal structure to obtaindifferent morphology structures. A morphology framework is used to characterise the aver-age mastic coating thickness around the main load carrying structure in the structures. Theuniaxial tension simulation shows that the mixtures with the lowest coating thickness exhibitbetter inter-particle interaction with more continuous load distribution chains between adja-cent aggregate particles, less stress concentrations and less strain localisation in the masticphase.

Place, publisher, year, edition, pages
Taylor & Francis, 2015
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-164891 (URN)10.1080/14680629.2015.1098561 (DOI)000379747600004 ()2-s2.0-84945206184 (Scopus ID)
Note

QC 20160204

Available from: 2015-04-20 Created: 2015-04-20 Last updated: 2017-12-04Bibliographically approved
3. Investigation of Energy-Based Crack Initiation Threshold from Meso-Scale Asphalt Concrete Response
Open this publication in new window or tab >>Investigation of Energy-Based Crack Initiation Threshold from Meso-Scale Asphalt Concrete Response
2016 (English)In: 8th RILEM International Conference on Mechanisms of Cracking and Debonding in Pavements, Springer Netherlands, 2016, p. 679-685Conference paper, Published paper (Refereed)
Abstract [en]

The existence of a fundamental energy threshold for meso-scale crackinitiation is investigated using micromechanical modeling techniques. X-rayComputed Tomography (CT) is used to acquire the internal structure of an asphaltconcrete mixture while Digital Image Processing (DIP) techniques is used to segment and analyze the different phases present in the mixture. Finite Element (FE)modeling is used to simulate a tensile loading condition to establish a critical micromechanical criterion for meso-scale crack initiation. The meso-scale asphaltconcrete mixture is subjected to different loading rates to obtain the global strainenergy density at the instance when the critical micromechanical crack-initiationcriterion threshold is attained at different deformation rates. The result from thestudy shows that there exists a fundamental global strain energy density thresholdthat is invariant of the rate of loading at the instance of meso-scale crack initiation.The result of this study also shows the potential of the use of X-Ray computedtomography in understanding the cracking phenomenon in asphalt mixture.

Place, publisher, year, edition, pages
Springer Netherlands, 2016
Series
RILEM Bookseries, ISSN 2211-0844 ; 13
Keyword
Micromechanical damage, Micro-crack initiation, Asphalt concrete, X-ray tomography
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-198660 (URN)10.1007/978-94-024-0867-6_95 (DOI)978-94-024-0866-9 (ISBN)978-94-024-0867-6 (ISBN)
Conference
8th RILEM International Conference on Mechanisms of Cracking and Debonding in Pavements
Funder
Swedish Transport Administration
Note

QC 20161220

Available from: 2016-12-19 Created: 2016-12-19 Last updated: 2016-12-20Bibliographically approved
4. Energy-Based Damage and Fracture Framework for Viscoelastic Asphalt Concrete
Open this publication in new window or tab >>Energy-Based Damage and Fracture Framework for Viscoelastic Asphalt Concrete
2015 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 145, p. 67-85Article in journal (Refereed) Published
Abstract [en]

A framework based on the continuum damage mechanics and thermodynamics of irreversible processes using internal state variables is used to characterize the distributed damage in viscoelastic asphalt materials in the form of micro-crack initiation and accumulation. At low temperatures and high deformation rates, micro-cracking is considered as the source of nonlinearity and thus the cause of deviation from linear viscoelastic response. Using a non-associated damage evolution law, the proposed model shows the ability to describe the temperature-dependent processes of micro-crack initiation, evolution and macro-crack formation with good comparison to the material response in the Superpave indirect tensile (IDT) strength test.

National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-164894 (URN)10.1016/j.engfracmech.2015.07.003 (DOI)000362612900005 ()2-s2.0-84937231899 (Scopus ID)
Note

Updated from submitted to published.

QC 20151104

Available from: 2015-04-20 Created: 2015-04-20 Last updated: 2017-12-04Bibliographically approved
5. Interpretation of the Superpave IDT strength test using a viscoelastic-damage constitutive model
Open this publication in new window or tab >>Interpretation of the Superpave IDT strength test using a viscoelastic-damage constitutive model
2016 (English)In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, p. 1-19Article in journal (Refereed) Published
Abstract [en]

This paper presents a new interpretation for the Superpave IDT strength test based on a viscoelastic-damage framework. The framework is based on continuum damage mechanics and the thermodynamics of irreversible processes with an anisotropic damage representation. The new approach introduces considerations for the viscoelastic effects and the damage accumulation that accompanies the fracture process in the interpretation of the Superpave IDT strength test for the identification of the Dissipated Creep Strain Energy (DCSE) limit from the test result. The viscoelastic model is implemented in a Finite Element Method (FEM) program for the simulation of the Superpave IDT strength test. The DCSE values obtained using the new approach is compared with the values obtained using the conventional approach to evaluate the validity of the assumptions made in the conventional interpretation of the test results. The result shows that the conventional approach over-estimates the DCSE value with increasing estimation error at higher deformation rates.

Place, publisher, year, edition, pages
Springer Netherlands, 2016
Keyword
Anisotropic damage, Asphalt concrete, Dissipated Creep Strain Energy (DCSE), Superpave IDT strength test, Visco-elastic-damage
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-187213 (URN)10.1007/s11043-016-9297-9 (DOI)000381982300010 ()2-s2.0-84961798950 (Scopus ID)
Note

QC 20161003

Available from: 2016-05-18 Created: 2016-05-18 Last updated: 2017-11-30Bibliographically approved
6. Damage and Fracture Characterization of Asphalt Concrete Mixtures using the Equivalent Micro-crack Stress Approac
Open this publication in new window or tab >>Damage and Fracture Characterization of Asphalt Concrete Mixtures using the Equivalent Micro-crack Stress Approac
(English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526Article in journal (Refereed) Submitted
Abstract [en]

In this paper, a new parameter termed ”equivalent micro-crack stress” (σmc) is proposed for characterizingthe cracking performance of asphalt mixtures. The ”equivalent micro-crack stress” (σmc) is a function ofthe material stiffness and a critical micro-crack initiation threshold (MCIT). The ”equivalent micro-crackstress” (σmc) takes a similar form as the failure stress obtained from the Griffith energy balance equation.The MCIT incorporates the influence of the fracture work and the size and spatial distribution of the airvoids in the determination of the material cracking performance. Experimental tests are carried out toobtain the (σmc) to characterize the cracking performance of unmodified and wax modified mixtures usingthe Superpave IDT tests at low temperature range (i.e. -20oC, -10oC and 0oC). The result shows that the ”equivalent micro-crack stress” (σmc) gives a good indication of the material cracking performance ofthe unmodified and wax modified mixtures. The result of numerical simulations of the fatigue behaviouralso shows that the relationship between the number of cycles to micro-crack formation (Nmc) and σmc can be used to distinguish the wax modified mixtures from the unmodified mixture.

Keyword
equivalent micro-crack stress, micro-crack initiation threshold, fracture analysis, asphalt concrete, damage characterization
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-198661 (URN)
Note

QS 201612

Available from: 2016-12-19 Created: 2016-12-19 Last updated: 2017-11-29Bibliographically approved
7. Continuum Plasticity Mechanics (CPM) - An energy-based plasticity model - Application to asphalt concrete mixtures.
Open this publication in new window or tab >>Continuum Plasticity Mechanics (CPM) - An energy-based plasticity model - Application to asphalt concrete mixtures.
(English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146Article in journal (Refereed) Submitted
Abstract [en]

A new generalized energy-based elasto-plastic constitutive model for both pressure-sensitive and pressure insensitive materials is developed and presented in this paper. The model is developed with the energy formulation which inherently captures the rate-sensitivity and can be used to model a wide range of materials ranging from rate-dependent materials such as polymers and asphalt concrete to rate-independent materials such as steel. No additional rate-dependency parameters is required to model rate dependent behaviour at different strain-rates. The new energy-based plasticity formulation takes a similar form as the conceptsused in continuum damage mechanics with the plastic strain transformed into a plasticity variable whichenters into the formulation to obtain the corresponding stress and strain due to the applied or subjected load conditions. The new energy-based plasticity formulation fits nicely into the thermodynamics framework thereby providing a true unifying framework for coupling damage and plasticity

Keyword
Continuum Plasticity Mechanics CPM, energy-based plasticity, plasticity variable, viscoplasticity
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-198662 (URN)
Note

QS 201612

Available from: 2016-12-19 Created: 2016-12-19 Last updated: 2017-11-29Bibliographically approved

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