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Marte Gutierrez - One of the best experts on this subject based on the ideXlab platform.

  • Influence of the intermediate principal stress and principal stress direction on the mechanical behavior of cohesionless soils using the discrete element method
    Computers and Geotechnics, 2017
    Co-Authors: Liangliang Chen, Marte Gutierrez
    Abstract:

    Abstract In this paper, the Discrete Element Method (DEM) is employed to numerically explore the response of hollow cylinder specimens of granular soils under complex stress paths. Two series of numerical tests are conducted to clarify the effects of the principal stress direction α and the intermediate principal stress through the b-value on the mechanical response of granular materials. The effects of α and b-value on the non-coaxiality of the principal stress and the principal Plastic Strain Increment directions are investigated. It is observed that b-value and α significantly affect the non-coaxial behavior of granular materials. Finally, the results are discussed and compared with those obtained from physical laboratory tests.

  • non coaxiality and energy dissipation in granular materials
    Soils and Foundations, 2000
    Co-Authors: Marte Gutierrez, Kenji Ishihara
    Abstract:

    ABSTRACT The paper presents a theoretical and experimental study of the effects of non-coaxiality or non-coincidence of the principal stress and the principal Plastic Strain Increment directions on the behaviour of granular materials. Experimental results from hollow cylindrical tests on sand involving principal stress rotation which support previously published results on non-coaxiality are presented. These results imply that constitutive relations cannot be sufficiently formulated in the principal stress space unless the deviations between the principal stress and Plastic Strain Increment directions are taken into consideration. It is shown that Plasticity formulations with Plastic potentials that are scalar functions of the stress invariants alone implicitly assume coaxiality and cannot be used for loading involving principal stress rotation. The paper presents a comprehensive analysis of the effects of non-coaxiality on the energy dissipation of sand. The paper shows that energy dissipation calculated from the principal stresses and the principal Plastic Strain Increments or from the stress and Plastic Strain Increment invariants, would be erroneous and would over-estimate the amount of dissipated energy during loading in the case of non-coaxial flow. A non-coaxiality factor is introduced in order to account for the effects of non-coaxiality on the energy dissipation equation and in a stress-dilatancy relation for granular materials. Explicit expressions of the non-coaxiality factor for two-and three-dimensional loading conditions are given at the end of the paper. Experimental results are presented to show the validity of the proposed energy dissipation and stress-dilatancy equations.

  • non coaxiality and energy dissipation in granular materials
    Soils and Foundations, 2000
    Co-Authors: Marte Gutierrez, Kenji Ishihara
    Abstract:

    ABSTRACT The paper presents a theoretical and experimental study of the effects of non-coaxiality or non-coincidence of the principal stress and the principal Plastic Strain Increment directions on the behaviour of granular materials. Experimental results from hollow cylindrical tests on sand involving principal stress rotation which support previously published results on non-coaxiality are presented. These results imply that constitutive relations cannot be sufficiently formulated in the principal stress space unless the deviations between the principal stress and Plastic Strain Increment directions are taken into consideration. It is shown that Plasticity formulations with Plastic potentials that are scalar functions of the stress invariants alone implicitly assume coaxiality and cannot be used for loading involving principal stress rotation. The paper presents a comprehensive analysis of the effects of non-coaxiality on the energy dissipation of sand. The paper shows that energy dissipation calculated from the principal stresses and the principal Plastic Strain Increments or from the stress and Plastic Strain Increment invariants, would be erroneous and would over-estimate the amount of dissipated energy during loading in the case of non-coaxial flow. A non-coaxiality factor is introduced in order to account for the effects of non-coaxiality on the energy dissipation equation and in a stress-dilatancy relation for granular materials. Explicit expressions of the non-coaxiality factor for two-and three-dimensional loading conditions are given at the end of the paper. Experimental results are presented to show the validity of the proposed energy dissipation and stress-dilatancy equations.

  • MODEL FOR THE DEFORMATION OF SAND DURING ROTATION OF PRINCIPAL STRESS DIRECTIONS
    Soils and Foundations, 1993
    Co-Authors: Marte Gutierrez, Kenji Ishihara, Ikuo Towhata
    Abstract:

    This paper presents an elastoPlastic constitutive model for the deformation of sand during loadings involving rotation of principal stress directions. The model employs a Plastic potential formulation that allows for the dependency of flow on the stress Increment direction and a stressdilatancy relation that incorporates the effects of the non-coaxiality of the principal stress and principal Plastic Strain Increment directions. The continuous Plastic deformation of sand during principal stress rotation at constant shear stress level is allowed for in the model by using a very small elastic region in the stress space. In the deviatoric stress space, an associated flow is employed to model the dependency of yielding on the stress Increment direction. Hardening behaviour is modelled using discrete surfaces of equal Plastic hardening modulus which are allowed to move with the stress point during loading. To model cyclic effects, the Plastic hardening modulus is allowed to stiffen during loading depending on the amount of accumulated normalized Plastic shear work. The model is used to simulate the deformation of hollow cylindrical sand specimens subjected to rotation of principal stress direction.

  • FLOW THEORY FOR SAND DURING ROTATION OF PRINCIPAL STRESS DIRECTION
    Soils and Foundations, 1991
    Co-Authors: Marte Gutierrez, Kenji Ishihara, Ikuo Towhata
    Abstract:

    The paper presents the results of a series of tests using the hollow cylindrical apparatus on the flow of sand during loadings involving rotation of principal stress direction. The results establish an important feature of the flow of sand during principal stress rotation, namely, nonuniqueness of flow or the dependency of the Plastic Strain Increment direction on the stress Increment direction. This feature contradicts the usual assumption in Plasticity theory of a unique flow during loadings causing Plastic deformations in a material. Guided by the results of the experiments, a Plastic potential theory capable of representing the dependency of the flow of sand on the stress Increment direction is proposed. Comparisons with the experimental results and the outcome of stress probe experiments show the validity of the proposed theory.

Ali Nayebi - One of the best experts on this subject based on the ideXlab platform.

  • Cyclic uniaxial and multiaxial loading with yield surface distortion consideration on prediction of ratcheting
    Mechanics of Materials, 2012
    Co-Authors: H. Rokhgireh, Ali Nayebi
    Abstract:

    Abstract In this study, the yield surface distortion was incorporated in the cyclic Plasticity modeling as well as its center movement. The combination of Chaboche’s model and the yield surface distortion model of Baltov was used in a set of uniaxial and multiaxial loadings. The variation of the stress amplitude and the mean stress and different multiaxial loadings such as tension-torsion tests were studied. It was shown that the consideration of the distortion of the yield surface via the distortion parameter and its sign in modeling has an important effect on the Plastic Strain Increment determination and so on the ratcheting rate. The combined model was applied to the experimental results. It was shown that the combination of the nonlinear kinematic hardening model of Chaboche and the yield surface distortion leads to a good estimation of the ratcheting Strain Increment in different uniaxial and multiaxial tests.

Ikuo Towhata - One of the best experts on this subject based on the ideXlab platform.

  • MODEL FOR THE DEFORMATION OF SAND DURING ROTATION OF PRINCIPAL STRESS DIRECTIONS
    Soils and Foundations, 1993
    Co-Authors: Marte Gutierrez, Kenji Ishihara, Ikuo Towhata
    Abstract:

    This paper presents an elastoPlastic constitutive model for the deformation of sand during loadings involving rotation of principal stress directions. The model employs a Plastic potential formulation that allows for the dependency of flow on the stress Increment direction and a stressdilatancy relation that incorporates the effects of the non-coaxiality of the principal stress and principal Plastic Strain Increment directions. The continuous Plastic deformation of sand during principal stress rotation at constant shear stress level is allowed for in the model by using a very small elastic region in the stress space. In the deviatoric stress space, an associated flow is employed to model the dependency of yielding on the stress Increment direction. Hardening behaviour is modelled using discrete surfaces of equal Plastic hardening modulus which are allowed to move with the stress point during loading. To model cyclic effects, the Plastic hardening modulus is allowed to stiffen during loading depending on the amount of accumulated normalized Plastic shear work. The model is used to simulate the deformation of hollow cylindrical sand specimens subjected to rotation of principal stress direction.

  • FLOW THEORY FOR SAND DURING ROTATION OF PRINCIPAL STRESS DIRECTION
    Soils and Foundations, 1991
    Co-Authors: Marte Gutierrez, Kenji Ishihara, Ikuo Towhata
    Abstract:

    The paper presents the results of a series of tests using the hollow cylindrical apparatus on the flow of sand during loadings involving rotation of principal stress direction. The results establish an important feature of the flow of sand during principal stress rotation, namely, nonuniqueness of flow or the dependency of the Plastic Strain Increment direction on the stress Increment direction. This feature contradicts the usual assumption in Plasticity theory of a unique flow during loadings causing Plastic deformations in a material. Guided by the results of the experiments, a Plastic potential theory capable of representing the dependency of the flow of sand on the stress Increment direction is proposed. Comparisons with the experimental results and the outcome of stress probe experiments show the validity of the proposed theory.

Hong-ki Hong - One of the best experts on this subject based on the ideXlab platform.

  • An endochronic theory accounted for deformation induced anisotropy
    International Journal of Plasticity, 1995
    Co-Authors: Hong-ki Hong
    Abstract:

    Abstract An anisotropic quadratic form of Plastic Strain Increment is used to define the intrinsic time in the endochronic theory of Plasticity. Based on this new definition, a yield function can be derived. This new version of endochronic theory can describe the expansion, translation, rotation, and distortion of the yield surface. While the initial yielding is in the form of the Mises yield criterion, the distortion of subsequent yield surfaces is expressed by the compression or stretching of the Mises yield surface. The effect of sharp front and blunt rear of the yield surface is considered to be of secondary importance and neglected in the interest of keeping the equations simple. This idealization will not much affect the prediction power of the model, because the Plastic Strain Increment is in the radial direction emanating from the center of the current yield surface and is not normal to the current yield surface. In this theory, the Plastic deformation is thus not sensitive to the exact shape of the yield surface. It has been shown that the proposed theory is capable of describing the experimental results of three different metals considered. The test series investigated include several different paths of prestress.

Samir Tiouajni - One of the best experts on this subject based on the ideXlab platform.

  • Deformation characteristics of dry hostun sand with principal stress axes rotation
    Soils and Foundations, 2011
    Co-Authors: Matthieu Blanc, Hervé Di Benedetto, Samir Tiouajni
    Abstract:

    Coaxiality between the principal directions of stress tensor and the principal directions of the Plastic Strain Increment tensor is assumed in conventional Plasticity models. In order to investigate coaxiality, or not, between these two principal directions, a series of drained tests on dry Hostun sand was carried out using a precision Hollow Cylinder Apparatus (HCA). The applied stress path includes large Principal Stress Axes Rotation (PSAR). Two of the three principal stresses are kept constant. So, among the three principal stresses, only the intermadiate principal stress which is the confining pressure (same pressure outside the hollow cylinder for internal and external lateral surfaces) changes during loading. During these tests, at different stress levels, the elastic (or quasi-elastic) properties are also investigated considering small amplitude quasi-static cycles. These small cycles are performed in two different directions by changing successively only the axial stress σzz or the shear stress σθz. The elastic experimental properties are well simulated using the DBGS hypo-elastic model, which takes into account PSAR. For each test, the elastic part of deformation is calculated using the DBGS model and removed from the global Strain to focus only on the irreversible part (Plastic part). Then, the principal directions of stress and the principal directions of Plastic Strain Increment are compared. The experimental results show that there is no coaxiality between these directions. This observation attests the existence of a non-coaxial Plasticity. In addition, coupling between coaxial and non-coaxial part is clearly shown. Experimental results reveal that the Plastic Strain part is very important for the first large amplitude cycles and remains greater than the elastic part even after 20 cycles.