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M Rappaz - One of the best experts on this subject based on the ideXlab platform.

  • 3 d granular modeling and in situ x ray tomographic imaging a comparative study of hot tearing formation and semi solid deformation in al cu alloys
    Acta Materialia, 2013
    Co-Authors: M Sistaninia, Jeanmarie Drezet, S Terzi, A B Phillion, M Rappaz
    Abstract:

    The mechanical behavior of partially solidified Al-Cu alloys is investigated to assess the influence of mushy zone deformation on hot tearing. For this purpose, the results of a semi-solid tensile test conducted in situ using X-ray microtomography are compared with the predictions of a coupled hydromechanical granular model in order to both validate the predictions of the model and explain the experimental observations. It is shown that hot tears initiate in the widest Liquid channels connected to the free (oxidized) surfaces as long as there is contact between the intergranular Liquid and the ambient air. The necking behavior is associated with the deformation-induced Liquid Pressure drop. Overall, the stresses predicted by the granular model under tensile and shear deformations agree well with the experimental data. Thus, the granular model achieves an important step in predicting hot tearing formation. (c) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • a granular model of equiaxed mushy zones formation of a coherent solid and localization of feeding
    Acta Materialia, 2006
    Co-Authors: Stephane Vernede, Philippe Jarry, M Rappaz
    Abstract:

    Abstract The gradual transformation of a mushy zone during alloy solidification, from a continuous Liquid film network to a fully coherent solid, has been simulated using a granular model. Based on a Voronoi tessellation of a random set of nucleation centres, solidification within each polyhedron is computed considering back-diffusion and coalescence. In the network of connected Liquid films, a Pressure drop calculation is performed assuming a Poiseuille flow in each channel, Kirchhoff’s conservation of flow at nodal points and flow losses compensating solidification shrinkage (KPL model). In addition to intergranular Liquid Pressure maps, the model shows the progressive formation of grain clusters, the localisation of the flow at very high solid fraction and thus natural transitions of the mushy zone.

P Aussillous - One of the best experts on this subject based on the ideXlab platform.

  • Granular collapse in a fluid: Role of the initial volume fraction
    Physics of Fluids, 2011
    Co-Authors: L Rondon, O Pouliquen, P Aussillous
    Abstract:

    The collapse of a granular column in a viscous Liquid is experimentally investigated. The morphology of the deposits is shown to be mainly controlled by the initial volume fraction of the granular mass and not by the aspect ratio of the column, an observation which differs from dry granular collapse. Two different regimes are identified corresponding to initially loose and dense packings. Loose packings give rise to thin and long deposits, the dynamics being fast. A positive Liquid Pressure is measured below the column. For dense packings, the runout distance is twice less, the flow is slow, and a negative pore Pressure is measured during the flow. These observations suggest that the dynamics of the granular collapse in a fluid is strongly affected by the dilatancy or contractancy behavior of the granular medium.

  • granular collapse in a fluid role of the initial volume fraction
    Bulletin of the American Physical Society, 2010
    Co-Authors: Lo Ic Rondon, O Pouliquen, P Aussillous
    Abstract:

    The collapse of a granular column in a viscous Liquid is experimentally investigated. The morphology of the deposits is shown to be mainly controlled by the initial volume fraction of the granular mass and not by the aspect ratio of the column, an observation which differs from dry granular collapse. Two different regimes are identified corresponding to initially loose and dense packings. Loose packings give rise to thin and long deposits, the dynamics being fast. A positive Liquid Pressure is measured below the column. For dense packings, the runout distance is twice less, the flow is slow, and a negative pore Pressure is measured during the flow. These observations suggest that the dynamics of the granular collapse in a fluid is strongly affected by the dilatancy or contractancy behavior of the granular medium. VC 2011 American Institute of Physics. [doi:10.1063/1.3594200]

Stephane Vernede - One of the best experts on this subject based on the ideXlab platform.

  • a granular model of equiaxed mushy zones formation of a coherent solid and localization of feeding
    Acta Materialia, 2006
    Co-Authors: Stephane Vernede, Philippe Jarry, M Rappaz
    Abstract:

    Abstract The gradual transformation of a mushy zone during alloy solidification, from a continuous Liquid film network to a fully coherent solid, has been simulated using a granular model. Based on a Voronoi tessellation of a random set of nucleation centres, solidification within each polyhedron is computed considering back-diffusion and coalescence. In the network of connected Liquid films, a Pressure drop calculation is performed assuming a Poiseuille flow in each channel, Kirchhoff’s conservation of flow at nodal points and flow losses compensating solidification shrinkage (KPL model). In addition to intergranular Liquid Pressure maps, the model shows the progressive formation of grain clusters, the localisation of the flow at very high solid fraction and thus natural transitions of the mushy zone.

O Pouliquen - One of the best experts on this subject based on the ideXlab platform.

  • Granular collapse in a fluid: Role of the initial volume fraction
    Physics of Fluids, 2011
    Co-Authors: L Rondon, O Pouliquen, P Aussillous
    Abstract:

    The collapse of a granular column in a viscous Liquid is experimentally investigated. The morphology of the deposits is shown to be mainly controlled by the initial volume fraction of the granular mass and not by the aspect ratio of the column, an observation which differs from dry granular collapse. Two different regimes are identified corresponding to initially loose and dense packings. Loose packings give rise to thin and long deposits, the dynamics being fast. A positive Liquid Pressure is measured below the column. For dense packings, the runout distance is twice less, the flow is slow, and a negative pore Pressure is measured during the flow. These observations suggest that the dynamics of the granular collapse in a fluid is strongly affected by the dilatancy or contractancy behavior of the granular medium.

  • granular collapse in a fluid role of the initial volume fraction
    Bulletin of the American Physical Society, 2010
    Co-Authors: Lo Ic Rondon, O Pouliquen, P Aussillous
    Abstract:

    The collapse of a granular column in a viscous Liquid is experimentally investigated. The morphology of the deposits is shown to be mainly controlled by the initial volume fraction of the granular mass and not by the aspect ratio of the column, an observation which differs from dry granular collapse. Two different regimes are identified corresponding to initially loose and dense packings. Loose packings give rise to thin and long deposits, the dynamics being fast. A positive Liquid Pressure is measured below the column. For dense packings, the runout distance is twice less, the flow is slow, and a negative pore Pressure is measured during the flow. These observations suggest that the dynamics of the granular collapse in a fluid is strongly affected by the dilatancy or contractancy behavior of the granular medium. VC 2011 American Institute of Physics. [doi:10.1063/1.3594200]

S. J. Yuan - One of the best experts on this subject based on the ideXlab platform.

  • Analysis of wrinkling during sheet hydroforming of curved surface shell considering reverse bulging effect
    International Journal of Mechanical Sciences, 2017
    Co-Authors: Y Z Chen, Yong Chao Xu, Weixiao Liu, Z. C. Zhang, S. J. Yuan
    Abstract:

    Wrinkling in unsupported region is a worthy problem to be solved in sheet metal forming process. Sheet hydroforming is advantageous in the prevention of unsupported wrinkles. However, the simply increasing of Liquid Pressure is not enough to suppress the wrinkling even though with the occurrence of ???reverse bulging effect???.1 In order to predict and control the wrinkling quantitatively in unsupported region for thin-walled shells with curved surface, a theoretical model on critical wrinkling stress was proposed by considering proper ???reverse bulging effect??? based on energy method. The influence of Liquid Pressure and other parameters on the critical wrinkling stress was analyzed. The critical loading path of the Liquid Pressure to control wrinkling was obtained by combining critical wrinkling stresses and circumferential stresses. An experimental setup for an extremely thin-walled shell with semi-ellipsoidal geometry was designed and manufactured to verify the theoretical model. It is found that at a certain punch stroke, the magnitude of the critical wrinkling stress increases and that of circumferential compressive stress decreases with the improvement of the Liquid Pressure. The critical loading path can be utilized to get well formed shells with a ratio of thickness to diameter equals 0.27% in the experiments. The proposed method can be applied to predict and control wrinkling in unsupported region for hydroforming of thin-walled shell with high accuracy and considerably reduced simulation time.