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Ludovic Noels - One of the best experts on this subject based on the ideXlab platform.

  • elastic damage to crack transition in a coupled non local implicit discontinuous galerkin extrinsic cohesive law framework
    Computer Methods in Applied Mechanics and Engineering, 2014
    Co-Authors: Ling Wu, Gauthier Becker, Ludovic Noels
    Abstract:

    Abstract One current challenge related to computational fracture mechanics is the modeling of ductile fracture and in particular the damage to crack transition. On the one hand, continuum damage models, especially in their non-local formulation which avoids the loss of solution uniqueness, can capture the Material Degradation Process up to the localization of the damage, but are unable to represent a discontinuity in the structure. On the other hand cohesive zone methods can represent the Process zone at the crack tip governing the crack propagation, but cannot account for the diffuse Material damaging Process. In this paper we propose to combine, in a small deformations setting, a non-local elastic damage model with a cohesive zone model. This combination is formulated within a discontinuous Galerkin finite element discretization. Indeed this DG weak formulation can easily be developed in a non-local implicit form and naturally embeds interface elements that can be used to integrate the traction separation law of the cohesive zone model. The method remains thus consistent and computationally efficient as compared to other cohesive element approaches. The effects of the damage to crack transition and of the mesh discretization are respectively studied on the compact tension specimen and on the double-notched specimen, demonstrating the efficiency and accuracy of the method.

  • Elastic damage to crack transition in a coupled non-local implicit discontinuous Galerkin/extrinsic cohesive law framework
    Computer Methods in Applied Mechanics and Engineering, 2014
    Co-Authors: Gauthier Becker, Ludovic Noels
    Abstract:

    Abstract One current challenge related to computational fracture mechanics is the modeling of ductile fracture and in particular the damage to crack transition. On the one hand, continuum damage models, especially in their non-local formulation which avoids the loss of solution uniqueness, can capture the Material Degradation Process up to the localization of the damage, but are unable to represent a discontinuity in the structure. On the other hand cohesive zone methods can represent the Process zone at the crack tip governing the crack propagation, but cannot account for the diffuse Material damaging Process. In this paper we propose to combine, in a small deformations setting, a non-local elastic damage model with a cohesive zone model. This combination is formulated within a discontinuous Galerkin finite element discretization. Indeed this DG weak formulation can easily be developed in a non-local implicit form and naturally embeds interface elements that can be used to integrate the traction separation law of the cohesive zone model. The method remains thus consistent and computationally efficient as compared to other cohesive element approaches. The effects of the damage to crack transition and of the mesh discretization are respectively studied on the compact tension specimen and on the double-notched specimen, demonstrating the efficiency and accuracy of the method.

Gauthier Becker - One of the best experts on this subject based on the ideXlab platform.

  • elastic damage to crack transition in a coupled non local implicit discontinuous galerkin extrinsic cohesive law framework
    Computer Methods in Applied Mechanics and Engineering, 2014
    Co-Authors: Ling Wu, Gauthier Becker, Ludovic Noels
    Abstract:

    Abstract One current challenge related to computational fracture mechanics is the modeling of ductile fracture and in particular the damage to crack transition. On the one hand, continuum damage models, especially in their non-local formulation which avoids the loss of solution uniqueness, can capture the Material Degradation Process up to the localization of the damage, but are unable to represent a discontinuity in the structure. On the other hand cohesive zone methods can represent the Process zone at the crack tip governing the crack propagation, but cannot account for the diffuse Material damaging Process. In this paper we propose to combine, in a small deformations setting, a non-local elastic damage model with a cohesive zone model. This combination is formulated within a discontinuous Galerkin finite element discretization. Indeed this DG weak formulation can easily be developed in a non-local implicit form and naturally embeds interface elements that can be used to integrate the traction separation law of the cohesive zone model. The method remains thus consistent and computationally efficient as compared to other cohesive element approaches. The effects of the damage to crack transition and of the mesh discretization are respectively studied on the compact tension specimen and on the double-notched specimen, demonstrating the efficiency and accuracy of the method.

  • Elastic damage to crack transition in a coupled non-local implicit discontinuous Galerkin/extrinsic cohesive law framework
    Computer Methods in Applied Mechanics and Engineering, 2014
    Co-Authors: Gauthier Becker, Ludovic Noels
    Abstract:

    Abstract One current challenge related to computational fracture mechanics is the modeling of ductile fracture and in particular the damage to crack transition. On the one hand, continuum damage models, especially in their non-local formulation which avoids the loss of solution uniqueness, can capture the Material Degradation Process up to the localization of the damage, but are unable to represent a discontinuity in the structure. On the other hand cohesive zone methods can represent the Process zone at the crack tip governing the crack propagation, but cannot account for the diffuse Material damaging Process. In this paper we propose to combine, in a small deformations setting, a non-local elastic damage model with a cohesive zone model. This combination is formulated within a discontinuous Galerkin finite element discretization. Indeed this DG weak formulation can easily be developed in a non-local implicit form and naturally embeds interface elements that can be used to integrate the traction separation law of the cohesive zone model. The method remains thus consistent and computationally efficient as compared to other cohesive element approaches. The effects of the damage to crack transition and of the mesh discretization are respectively studied on the compact tension specimen and on the double-notched specimen, demonstrating the efficiency and accuracy of the method.

S.m. Schlögl - One of the best experts on this subject based on the ideXlab platform.

  • Numerical study of microstructural evolution in low alloy Cr-Mo steels during hydrogen attack
    2003
    Co-Authors: S.m. Schlögl, E. Van Der Giessen
    Abstract:

    Hydrogen attack is a Material Degradation Process which involves partial dissolution of the microstructure in favor of the growth of methane filled cavities. Two numerical models are discussed to study this multi-physics Process: a simple one-dimensional model and the start of a more sophisticated microstructural model solved by a finite element technique. The first model shows that hydrogen attack involves a strong coupling between dissolution and cavity growth. The more elaborate model will be used to assess the validity of the assumptions of the first model.

  • Computational model for carbon diffusion and methane formation in a ferritic steel during hydrogen attack
    Scripta Materialia, 2002
    Co-Authors: S.m. Schlögl, E. Van Der Giessen
    Abstract:

    Abstract Hydrogen attack is a Material Degradation Process which involves partial dissolution of the microstructure in favor of the growth of methane-filled cavities. The various physical–chemical Processes involved are strongly coupled. We present a numerical microstructural model for two of these Processes, based on a variational approach.

  • Micromechanics of high temperature hydrogen attack
    International Journal for Numerical Methods in Engineering, 2001
    Co-Authors: S.m. Schlögl, Erik Van Der Giessen
    Abstract:

    Hydrogen attack is a Material Degradation Process that occurs at elevated temperatures in hydrogen-rich environments, such as found in petrochemical installations. Weldments in components such as reactor vessels are particularly susceptible to hydrogen attack. This paper discusses a multi-scale micromechanics modelling approach in which the chemico-mechanical damage Processes at sub-micron scale are coupled to the macroscopic behaviour through a series of size-scale transitions. A simulation of hydrogen attack in a welded reactor serves as an illustration of the approach. Copyright © 2001 John Wiley & Sons, Ltd.

  • Evolution of the methane pressure in a standard 2.25Cr-1Mo steel during hydrogen attack
    Acta Materialia, 2001
    Co-Authors: S.m. Schlögl, Jiří Svoboda, Van Der Erik Giessen
    Abstract:

    The Material Degradation Process hydrogen attack has its origin in the dissolved hydrogen which reacts with the carbon of the steel to form methane inside grain boundary cavities. Hydrogen attack involves several interacting Processes such as diffusion of carbon and of the metal atoms; dissolution of carbides; reaction of C with H to methane; dislocation creep and grain boundary diffusion. In this paper, a microstructural model is presented which takes into account the above-mentioned Processes within the framework of a multi-component, multi-phase continuum description. The numerical model is developed for microstructures build up by a ferritic matrix and carbides such as M7C3 and M23C6. The model is applied to predict the microstructural evolution, the growth of cavities and the resulting methane pressure in standard 2.25Cr–1Mo steel during hydrogen exposure at 500°C. They show that cavity growth and methane generation are strongly coupled, thus falsifying previous decoupled approaches to hydrogen attack.

Ling Wu - One of the best experts on this subject based on the ideXlab platform.

  • elastic damage to crack transition in a coupled non local implicit discontinuous galerkin extrinsic cohesive law framework
    Computer Methods in Applied Mechanics and Engineering, 2014
    Co-Authors: Ling Wu, Gauthier Becker, Ludovic Noels
    Abstract:

    Abstract One current challenge related to computational fracture mechanics is the modeling of ductile fracture and in particular the damage to crack transition. On the one hand, continuum damage models, especially in their non-local formulation which avoids the loss of solution uniqueness, can capture the Material Degradation Process up to the localization of the damage, but are unable to represent a discontinuity in the structure. On the other hand cohesive zone methods can represent the Process zone at the crack tip governing the crack propagation, but cannot account for the diffuse Material damaging Process. In this paper we propose to combine, in a small deformations setting, a non-local elastic damage model with a cohesive zone model. This combination is formulated within a discontinuous Galerkin finite element discretization. Indeed this DG weak formulation can easily be developed in a non-local implicit form and naturally embeds interface elements that can be used to integrate the traction separation law of the cohesive zone model. The method remains thus consistent and computationally efficient as compared to other cohesive element approaches. The effects of the damage to crack transition and of the mesh discretization are respectively studied on the compact tension specimen and on the double-notched specimen, demonstrating the efficiency and accuracy of the method.

E. Van Der Giessen - One of the best experts on this subject based on the ideXlab platform.

  • Numerical study of microstructural evolution in low alloy Cr-Mo steels during hydrogen attack
    2003
    Co-Authors: S.m. Schlögl, E. Van Der Giessen
    Abstract:

    Hydrogen attack is a Material Degradation Process which involves partial dissolution of the microstructure in favor of the growth of methane filled cavities. Two numerical models are discussed to study this multi-physics Process: a simple one-dimensional model and the start of a more sophisticated microstructural model solved by a finite element technique. The first model shows that hydrogen attack involves a strong coupling between dissolution and cavity growth. The more elaborate model will be used to assess the validity of the assumptions of the first model.

  • Computational model for carbon diffusion and methane formation in a ferritic steel during hydrogen attack
    Scripta Materialia, 2002
    Co-Authors: S.m. Schlögl, E. Van Der Giessen
    Abstract:

    Abstract Hydrogen attack is a Material Degradation Process which involves partial dissolution of the microstructure in favor of the growth of methane-filled cavities. The various physical–chemical Processes involved are strongly coupled. We present a numerical microstructural model for two of these Processes, based on a variational approach.

  • A continuum damage analysis of hydrogen attack in a 2.25Cr–1Mo pressure vessel
    Materials Science and Engineering: A, 1998
    Co-Authors: M.w.d. Van Der Burg, E. Van Der Giessen, Viggo Tvergaard
    Abstract:

    A micromechanically based continuum damage model is presented to analyze the stress, temperature and hydrogen pressure dependent Material Degradation Process termed hydrogen attack, inside a pressure vessel. Hydrogen attack (HA) is the damage Process of grain boundary facets due to a chemical reaction of carbides with hydrogen, thus forming cavities with high pressure methane gas. Driven by the methane gas pressure, the cavities grow, while remote tensile stresses can significantly enhance the cavitation rate. The damage model gives the strain-rate and damage rate as a function of the temperature, hydrogen pressure and applied stresses. The model is applied to study HA in a vessel wall, where nonuniform distributions of hydrogen pressure, temperature and stresses result in a nonuniform damage distribution over the vessel wall. Stresses inside the vessel wall first tend to accelerate and later decelerate the cavitation rate significantly. Numerical studies for different Material parameters and different stress conditions demonstrate the HA Process inside a vessel in time. Also, the lifetime of the pressure vessel is determined. The analyses underline that the general applicability of the Nelson curve is questionable