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Masoud K Darabi - One of the best experts on this subject based on the ideXlab platform.

  • a thermodynamic framework for constitutive modeling of time and rate dependent materials part ii numerical aspects and application to asphalt concrete
    International Journal of Plasticity, 2012
    Co-Authors: Masoud K Darabi, Eyad Masad, Rashid Abu K Alrub, Dallas N Little
    Abstract:

    In this paper, we present within the finite element context the numerical algorithm for the integration of the thermodynamically consistent thermo-viscoelastic, thermo-viscoplastic, thermo-viscodamage, and thermo-healing constitutive equations derived in the first part of this paper. The nonlinear viscoelastic model is implemented using a recursive-iterative algorithm, whereas an extension of the classical rate-independent return mapping algorithm to the rate-dependent problems is used for numerical implementation of the viscoplasticity model. Moreover, the healing Natural Configuration along with the power transformation equivalence hypothesis, proposed in the first part of the paper, are used for the implementation of the viscodamage and micro-damage healing models. Hence, the thermo-viscoelastic and thermo-viscoplastic models are also implemented in the healing Configuration. These numerical algorithms are implemented in the well-known finite element code Abaqus via the user material subroutine UMAT. A systematic procedure for identification of model parameters is presented. The model is then used to simulate the time-, temperature-, and rate-dependent response of asphalt concrete over an extensive set of experimental measurements including creep-recovery, creep, triaxial, constant strain rate, and repeated creep-recovery tests in both tension and compression. Comparisons of the model predictions and the experimental measurements show that the model is capable of predicting the nonlinear behavior of asphalt concrete subjected to different loading conditions.

  • a thermodynamic framework for constitutive modeling of time and rate dependent materials part i theory
    International Journal of Plasticity, 2012
    Co-Authors: Rashid Abu K Alrub, Masoud K Darabi
    Abstract:

    A general thermodynamic-based framework for deriving coupled temperature-dependent viscoelasticity, viscoplasticity, viscodamage, and micro-damage healing constitutive models for constitutive modeling of time- and rate-dependent materials is presented. Principle of virtual power, Clausius–Duhem inequality, and the principle of maximum rate of dissipation are used to construct this general thermodynamic framework. A micro-damage healing Natural Configuration is introduced to enhance the continuum damage mechanics theories in modeling the healing phenomenon. This healing Configuration can be considered as the extension of the well-known Kachanov’s effective (undamaged) Configuration (Kachanov, 1958). The viscoplasticity loading condition is defined from the microforce balance derived directly from the principle of virtual power. Moreover, for the first time, viscoelasticity, viscodamage, and micro-damage healing microforce balances are derived directly from the principle of virtual power. It is also shown that the generalized non-associative plasticity/viscoplasticity theories can be a direct consequence of postulating the principle of virtual power. The emphasis in this paper is placed on the decomposition of thermodynamic conjugate forces into energetic and dissipative components. It is shown that this decomposition is necessary for accurate estimation of the rate of energy dissipation. The energetic components are related to the Helmholtz free energy, whereas the dissipative components are related to the rate of energy dissipation. This thermodynamic framework is used for deriving more comprehensive viscoelastic, viscoplastic, and viscodamage, and micro-damage healing constitutive models.

  • a continuum damage mechanics framework for modeling micro damage healing
    International Journal of Solids and Structures, 2012
    Co-Authors: Masoud K Darabi, Rashid Abu K Alrub, Dallas N Little
    Abstract:

    A novel continuum damage mechanics-based framework is proposed to model the micro-damage healing phenomenon in the materials that tend to self-heal. This framework extends the well-known Kachanov’s (1958) effective Configuration and the concept of the effective stress space to self-healing materials by introducing the healing Natural Configuration in order to incorporate the micro-damage healing effects. Analytical relations are derived to relate strain tensors and tangent stiffness moduli in the nominal and healing Configurations for each postulated transformation hypothesis (i.e. strain, elastic strain energy, and power equivalence hypotheses). The ability of the proposed model to explain micro-damage healing is demonstrated by presenting several examples. Also, a general thermodynamic framework for constitutive modeling of damage and micro-damage healing mechanisms is presented.

  • a micro damage healing model that improves prediction of fatigue life in asphalt mixes
    International Journal of Engineering Science, 2010
    Co-Authors: Rashid Abu K Alrub, Eyad Masad, Masoud K Darabi, Dallas N Little
    Abstract:

    Abstract The focus of the current paper is on the development and validation of a micro-damage healing model that improves the ability of an integrated nonlinear viscoelastic, viscoplastic, and viscodamage constitutive model based on continuum damage mechanics for predicting the fatigue life of asphalt paving mixtures. The model parameters of the continuum-based healing model are related to fundamental material properties. Recursive–iterative and radial return algorithms are used for the numerical implementation of viscoelasticity and viscoplasticity models respectively, whereas the viscodamage and micro-damage healing models are implemented using the concept of the effective undamaged-healed Natural Configuration. Numerical algorithms are implemented into the well-known finite element code Abaqus via the user material subroutine UMAT. Finally, the model is validated by comparing its predictions with experimental data on an asphalt mix that include repeated creep-recovery tests for different loading times and rest periods in both tension and compression. The significant enhancement of the ability of the constitutive model to predict fatigue life due to inclusion of the micro-damage healing is clearly demonstrated.

Dallas N Little - One of the best experts on this subject based on the ideXlab platform.

  • a thermodynamic framework for constitutive modeling of time and rate dependent materials part ii numerical aspects and application to asphalt concrete
    International Journal of Plasticity, 2012
    Co-Authors: Masoud K Darabi, Eyad Masad, Rashid Abu K Alrub, Dallas N Little
    Abstract:

    In this paper, we present within the finite element context the numerical algorithm for the integration of the thermodynamically consistent thermo-viscoelastic, thermo-viscoplastic, thermo-viscodamage, and thermo-healing constitutive equations derived in the first part of this paper. The nonlinear viscoelastic model is implemented using a recursive-iterative algorithm, whereas an extension of the classical rate-independent return mapping algorithm to the rate-dependent problems is used for numerical implementation of the viscoplasticity model. Moreover, the healing Natural Configuration along with the power transformation equivalence hypothesis, proposed in the first part of the paper, are used for the implementation of the viscodamage and micro-damage healing models. Hence, the thermo-viscoelastic and thermo-viscoplastic models are also implemented in the healing Configuration. These numerical algorithms are implemented in the well-known finite element code Abaqus via the user material subroutine UMAT. A systematic procedure for identification of model parameters is presented. The model is then used to simulate the time-, temperature-, and rate-dependent response of asphalt concrete over an extensive set of experimental measurements including creep-recovery, creep, triaxial, constant strain rate, and repeated creep-recovery tests in both tension and compression. Comparisons of the model predictions and the experimental measurements show that the model is capable of predicting the nonlinear behavior of asphalt concrete subjected to different loading conditions.

  • a continuum damage mechanics framework for modeling micro damage healing
    International Journal of Solids and Structures, 2012
    Co-Authors: Masoud K Darabi, Rashid Abu K Alrub, Dallas N Little
    Abstract:

    A novel continuum damage mechanics-based framework is proposed to model the micro-damage healing phenomenon in the materials that tend to self-heal. This framework extends the well-known Kachanov’s (1958) effective Configuration and the concept of the effective stress space to self-healing materials by introducing the healing Natural Configuration in order to incorporate the micro-damage healing effects. Analytical relations are derived to relate strain tensors and tangent stiffness moduli in the nominal and healing Configurations for each postulated transformation hypothesis (i.e. strain, elastic strain energy, and power equivalence hypotheses). The ability of the proposed model to explain micro-damage healing is demonstrated by presenting several examples. Also, a general thermodynamic framework for constitutive modeling of damage and micro-damage healing mechanisms is presented.

  • a micro damage healing model that improves prediction of fatigue life in asphalt mixes
    International Journal of Engineering Science, 2010
    Co-Authors: Rashid Abu K Alrub, Eyad Masad, Masoud K Darabi, Dallas N Little
    Abstract:

    Abstract The focus of the current paper is on the development and validation of a micro-damage healing model that improves the ability of an integrated nonlinear viscoelastic, viscoplastic, and viscodamage constitutive model based on continuum damage mechanics for predicting the fatigue life of asphalt paving mixtures. The model parameters of the continuum-based healing model are related to fundamental material properties. Recursive–iterative and radial return algorithms are used for the numerical implementation of viscoelasticity and viscoplasticity models respectively, whereas the viscodamage and micro-damage healing models are implemented using the concept of the effective undamaged-healed Natural Configuration. Numerical algorithms are implemented into the well-known finite element code Abaqus via the user material subroutine UMAT. Finally, the model is validated by comparing its predictions with experimental data on an asphalt mix that include repeated creep-recovery tests for different loading times and rest periods in both tension and compression. The significant enhancement of the ability of the constitutive model to predict fatigue life due to inclusion of the micro-damage healing is clearly demonstrated.

Eyad Masad - One of the best experts on this subject based on the ideXlab platform.

  • a thermodynamic framework for constitutive modeling of time and rate dependent materials part ii numerical aspects and application to asphalt concrete
    International Journal of Plasticity, 2012
    Co-Authors: Masoud K Darabi, Eyad Masad, Rashid Abu K Alrub, Dallas N Little
    Abstract:

    In this paper, we present within the finite element context the numerical algorithm for the integration of the thermodynamically consistent thermo-viscoelastic, thermo-viscoplastic, thermo-viscodamage, and thermo-healing constitutive equations derived in the first part of this paper. The nonlinear viscoelastic model is implemented using a recursive-iterative algorithm, whereas an extension of the classical rate-independent return mapping algorithm to the rate-dependent problems is used for numerical implementation of the viscoplasticity model. Moreover, the healing Natural Configuration along with the power transformation equivalence hypothesis, proposed in the first part of the paper, are used for the implementation of the viscodamage and micro-damage healing models. Hence, the thermo-viscoelastic and thermo-viscoplastic models are also implemented in the healing Configuration. These numerical algorithms are implemented in the well-known finite element code Abaqus via the user material subroutine UMAT. A systematic procedure for identification of model parameters is presented. The model is then used to simulate the time-, temperature-, and rate-dependent response of asphalt concrete over an extensive set of experimental measurements including creep-recovery, creep, triaxial, constant strain rate, and repeated creep-recovery tests in both tension and compression. Comparisons of the model predictions and the experimental measurements show that the model is capable of predicting the nonlinear behavior of asphalt concrete subjected to different loading conditions.

  • a micro damage healing model that improves prediction of fatigue life in asphalt mixes
    International Journal of Engineering Science, 2010
    Co-Authors: Rashid Abu K Alrub, Eyad Masad, Masoud K Darabi, Dallas N Little
    Abstract:

    Abstract The focus of the current paper is on the development and validation of a micro-damage healing model that improves the ability of an integrated nonlinear viscoelastic, viscoplastic, and viscodamage constitutive model based on continuum damage mechanics for predicting the fatigue life of asphalt paving mixtures. The model parameters of the continuum-based healing model are related to fundamental material properties. Recursive–iterative and radial return algorithms are used for the numerical implementation of viscoelasticity and viscoplasticity models respectively, whereas the viscodamage and micro-damage healing models are implemented using the concept of the effective undamaged-healed Natural Configuration. Numerical algorithms are implemented into the well-known finite element code Abaqus via the user material subroutine UMAT. Finally, the model is validated by comparing its predictions with experimental data on an asphalt mix that include repeated creep-recovery tests for different loading times and rest periods in both tension and compression. The significant enhancement of the ability of the constitutive model to predict fatigue life due to inclusion of the micro-damage healing is clearly demonstrated.

  • modelling sand asphalt mixtures within a thermodynamic framework theory and application to torsion experiments
    International Journal of Pavement Engineering, 2009
    Co-Authors: Parag Ravindran, J.m. Krishnan, Eyad Masad, K R Rajagopal
    Abstract:

    Sand–asphalt mixtures are difficult to model, partly due to their composition and partly due to the complex interplay among their constituents. This work is concerned with the development of an anisotropic model to describe the nonlinear behaviour of sand–asphalt mixtures. A general thermodynamic framework is used, which allows for the material to have multiple Natural Configurations corresponding to its underlying structure. The evolution of the Natural Configuration takes place in a thermodynamically consistent manner. The model developed is corroborated using experimental results published by Ravindran et al. (2007a,b) on torsion tests of sand–asphalt specimens over a range of conditions.

Rashid Abu K Alrub - One of the best experts on this subject based on the ideXlab platform.

  • a thermodynamic framework for constitutive modeling of time and rate dependent materials part ii numerical aspects and application to asphalt concrete
    International Journal of Plasticity, 2012
    Co-Authors: Masoud K Darabi, Eyad Masad, Rashid Abu K Alrub, Dallas N Little
    Abstract:

    In this paper, we present within the finite element context the numerical algorithm for the integration of the thermodynamically consistent thermo-viscoelastic, thermo-viscoplastic, thermo-viscodamage, and thermo-healing constitutive equations derived in the first part of this paper. The nonlinear viscoelastic model is implemented using a recursive-iterative algorithm, whereas an extension of the classical rate-independent return mapping algorithm to the rate-dependent problems is used for numerical implementation of the viscoplasticity model. Moreover, the healing Natural Configuration along with the power transformation equivalence hypothesis, proposed in the first part of the paper, are used for the implementation of the viscodamage and micro-damage healing models. Hence, the thermo-viscoelastic and thermo-viscoplastic models are also implemented in the healing Configuration. These numerical algorithms are implemented in the well-known finite element code Abaqus via the user material subroutine UMAT. A systematic procedure for identification of model parameters is presented. The model is then used to simulate the time-, temperature-, and rate-dependent response of asphalt concrete over an extensive set of experimental measurements including creep-recovery, creep, triaxial, constant strain rate, and repeated creep-recovery tests in both tension and compression. Comparisons of the model predictions and the experimental measurements show that the model is capable of predicting the nonlinear behavior of asphalt concrete subjected to different loading conditions.

  • a thermodynamic framework for constitutive modeling of time and rate dependent materials part i theory
    International Journal of Plasticity, 2012
    Co-Authors: Rashid Abu K Alrub, Masoud K Darabi
    Abstract:

    A general thermodynamic-based framework for deriving coupled temperature-dependent viscoelasticity, viscoplasticity, viscodamage, and micro-damage healing constitutive models for constitutive modeling of time- and rate-dependent materials is presented. Principle of virtual power, Clausius–Duhem inequality, and the principle of maximum rate of dissipation are used to construct this general thermodynamic framework. A micro-damage healing Natural Configuration is introduced to enhance the continuum damage mechanics theories in modeling the healing phenomenon. This healing Configuration can be considered as the extension of the well-known Kachanov’s effective (undamaged) Configuration (Kachanov, 1958). The viscoplasticity loading condition is defined from the microforce balance derived directly from the principle of virtual power. Moreover, for the first time, viscoelasticity, viscodamage, and micro-damage healing microforce balances are derived directly from the principle of virtual power. It is also shown that the generalized non-associative plasticity/viscoplasticity theories can be a direct consequence of postulating the principle of virtual power. The emphasis in this paper is placed on the decomposition of thermodynamic conjugate forces into energetic and dissipative components. It is shown that this decomposition is necessary for accurate estimation of the rate of energy dissipation. The energetic components are related to the Helmholtz free energy, whereas the dissipative components are related to the rate of energy dissipation. This thermodynamic framework is used for deriving more comprehensive viscoelastic, viscoplastic, and viscodamage, and micro-damage healing constitutive models.

  • a continuum damage mechanics framework for modeling micro damage healing
    International Journal of Solids and Structures, 2012
    Co-Authors: Masoud K Darabi, Rashid Abu K Alrub, Dallas N Little
    Abstract:

    A novel continuum damage mechanics-based framework is proposed to model the micro-damage healing phenomenon in the materials that tend to self-heal. This framework extends the well-known Kachanov’s (1958) effective Configuration and the concept of the effective stress space to self-healing materials by introducing the healing Natural Configuration in order to incorporate the micro-damage healing effects. Analytical relations are derived to relate strain tensors and tangent stiffness moduli in the nominal and healing Configurations for each postulated transformation hypothesis (i.e. strain, elastic strain energy, and power equivalence hypotheses). The ability of the proposed model to explain micro-damage healing is demonstrated by presenting several examples. Also, a general thermodynamic framework for constitutive modeling of damage and micro-damage healing mechanisms is presented.

  • a micro damage healing model that improves prediction of fatigue life in asphalt mixes
    International Journal of Engineering Science, 2010
    Co-Authors: Rashid Abu K Alrub, Eyad Masad, Masoud K Darabi, Dallas N Little
    Abstract:

    Abstract The focus of the current paper is on the development and validation of a micro-damage healing model that improves the ability of an integrated nonlinear viscoelastic, viscoplastic, and viscodamage constitutive model based on continuum damage mechanics for predicting the fatigue life of asphalt paving mixtures. The model parameters of the continuum-based healing model are related to fundamental material properties. Recursive–iterative and radial return algorithms are used for the numerical implementation of viscoelasticity and viscoplasticity models respectively, whereas the viscodamage and micro-damage healing models are implemented using the concept of the effective undamaged-healed Natural Configuration. Numerical algorithms are implemented into the well-known finite element code Abaqus via the user material subroutine UMAT. Finally, the model is validated by comparing its predictions with experimental data on an asphalt mix that include repeated creep-recovery tests for different loading times and rest periods in both tension and compression. The significant enhancement of the ability of the constitutive model to predict fatigue life due to inclusion of the micro-damage healing is clearly demonstrated.

Yungchi Cheng - One of the best experts on this subject based on the ideXlab platform.

  • phosphorylation of pyrimidine deoxynucleoside analog diphosphates selective phosphorylation of l nucleoside analog diphosphates by 3 phosphoglycerate kinase
    Journal of Biological Chemistry, 2002
    Co-Authors: Preethi Krishnan, Qin Fu, Jiehyuan Liou, Ginger E Dutschman, Yungchi Cheng
    Abstract:

    Abstract d-Nucleoside analogs, which are in the Natural Configuration, as well as the l-nucleoside analogs, are clinically relevant antiviral and anticancer agents. Metabolism of l-nucleoside analog diphosphates to the triphosphates, however, remains unexplored. Studies with recombinant nm23-H1 and -H2 isoforms indicated that l-nucleoside analog diphosphates were not phosphorylated by their nucleoside diphosphate kinase (NDPK) activity. Therefore, roles of creatine kinase, 3-phosphoglycerate kinase, and pyruvate kinase were evaluated using preparations from commercial sources and human HepG2 cells. Phosphorylation of l-OddC, l-SddC,l-Fd4C, l-FMAU, and l-ddC were compared with d-deoxynucleoside analogs, AraC, dFdC, andd-FMAU, and d-dideoxynucleoside analogs, ddC and d4T. Results based on preparations from HepG2 cells showed thatl-nucleoside analog diphosphates were selectively phosphorylated by 3-phosphoglycerate kinase, whereas,d-deoxynucleoside analog diphosphates were phosphorylated by NDPK. Interestingly, ddCDP and d4TDP were substrates for creatine kinase, but were not phosphorylated by NDPK. In conclusion, it is proposed that specificity of the phosphorylating enzymes toward the nucleoside analog diphosphates is dependent on the Configuration of the analog (l or d) and the presence or absence of 3′-hydroxyl group in the sugar moiety. The enzymatic process of phosphorylation of l- and d-nucleoside analog diphosphates is different in cells.