References of "Keller, Clément"
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See detailFinite element analysis of the free surface effects on the mechanical behavior of thin nickel polycrystals
Keller, Clément ULg; Hug, eric; Habraken, Anne ULg et al

in International Journal of Plasticity (2012), 29

The miniaturization of metallic samples has been proved to deeply affect their mechanical properties leading to a softening or a hardening effect depending on the order of the dimension reduction. The ... [more ▼]

The miniaturization of metallic samples has been proved to deeply affect their mechanical properties leading to a softening or a hardening effect depending on the order of the dimension reduction. The objective of this work is to provide new numerical results which explain the softening mechanisms on the mechanical behavior for nickel polycrystals which have been experimentally characterized by the authors in a previous published paper (Keller et al., 2011). Based on a strain gradient crystalline plasticity model identified for nickel, simulations of tensile tests were performed for samples with different thicknesses and grain sizes. The simulations correctly reproduce the softening effect linked to a decrease in the thickness and in the number of grains across the thickness. The analysis of the plasticity mechanisms shows that the softening is due to surface effects which are discussed in terms of grain orientations, dislocation mean free path and long-range back-stress. The model also predicts a hardening mechanism for further dimension reduction if the samples have only grain boundaries perpendicular to the tensile direction. In this case, the modification of the mechanical behavior is due to strain gradients formation. [less ▲]

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See detailMicrostructural size effects on mechanical properties of high purity nickel
Keller, Clément ULg; Hug, E.; Feaugas, X.

in International Journal of Plasticity (2011), 27

The aim of this article is to provide experimental results in order to understand the microstructural size effects which occur with a decrease in the thickness of polycrystalline nickel samples from 3.2 ... [more ▼]

The aim of this article is to provide experimental results in order to understand the microstructural size effects which occur with a decrease in the thickness of polycrystalline nickel samples from 3.2 mm to 12.5 lm. The influence of the thickness, grain size and ratio thickness to grain size on the mechanical properties and strain hardening were investigated by mechanical tests and TEM observations. The results show the presence of three different domains of mechanical behaviour: polycrystalline, multicrystalline and quasi-single crystalline depending on the thickness and on the number of grains across the thickness. The transition between the three domains is due to the occurrence of surface effects involving a decrease in the long-range internal backstress revealed by the TEM observations. [less ▲]

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See detailTowards the Prediction of Damage Of Peritectic Steels During Continuous Casting Process
Keller, Clément ULg; Schwartz, Renée; Bobadilla, Manuel et al

in AIP Conference Proceedings (2011), 1353

In the Continuous Casting process, products are sometimes rejected or called defective due to the presence of transversal cracks. This type of macroscopic damage is expected to be due to a ductility loss ... [more ▼]

In the Continuous Casting process, products are sometimes rejected or called defective due to the presence of transversal cracks. This type of macroscopic damage is expected to be due to a ductility loss during cooling in the bending and unbending areas of the CC line. In order to study this damage, a 2D model has been developed to predict at the mesoscopic level the intergranular crack event taking into account the creep and diffusion of voids. Already validated for a microalloyed steel, the model is identified and used in this study to predict the crack formation for three different grades of peritectic steels. Results show encouraging predictions of the damage. [less ▲]

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See detailInfluence of Surface Effect On Nickel Micro Deep Drawing Process
Keller, Clément ULg; Afteni, Mitica; Banu, Mihaela et al

in Proceeding of the Numiform 2010 conference (2010)

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See detailEffect of a decrease in sample dimensions on plasticity: application to the micro-forming of nickel
Keller, Clément ULg; Afteni, Mitica; Banu, M. et al

in Steel Research International (2010), 81(9), 1173-1177

The mechanical behavior of polycrystalline nickel is investigated in tension as a function of the dimensions. Experimental tests and finite element simulations with a crystalline plasticity code are ... [more ▼]

The mechanical behavior of polycrystalline nickel is investigated in tension as a function of the dimensions. Experimental tests and finite element simulations with a crystalline plasticity code are carried out for samples with thicknesses ranging between 12.5 μm and 3.2 mm and grain size around 100 μm. Results show three different kinds of behavior depending on the number of grains across the thickness due to the apparition of stress and dislocation density gradients. Bulge tests are then used to study the formability of nickel polycrystals with thickness lower than 400 μm. [less ▲]

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See detailMiniaturization induced size effects: Experimental and numerical investigation of size effects linked to the miniaturization of metallic components
Keller, Clément ULg; Habraken, Anne ULg; Hug, E. et al

in Scale transition for plastic crystalline and microstructured materials: from experiment to numerical modeling (2010)

The manufacturing of small metallic components for MEMS is a great challenge for industries. However, the lack of knowledge about the mechanical behavior of metals when they are employed in small ... [more ▼]

The manufacturing of small metallic components for MEMS is a great challenge for industries. However, the lack of knowledge about the mechanical behavior of metals when they are employed in small components can reduce the economical development of MEMS due to manufacturing and reliability issues. The objective of this work is to provide new scientific results to improve the understanding of the mechanical properties of micro-components. Experimental and numerical (strain gradient plasticity model) tensile tests are performed on thin nickel single crystals and polycrystals (thickness larger than 10 m) showing different size effects depending on the dimensions of the samples. These effects are then taken into account in new simplified numerical models for the prediction of micro-forming processes. [less ▲]

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See detailInfluence of Surface Effect on Nickel Micro Deep Drawing Process
Keller, Clément ULg; Afteni, Mitica; Banu, M. et al

in NUMIFORM 2010, VOLS 1 AND 2 (2010)

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See detailInfluence of the temperature on the tensile behaviour of a modified 9Cr–1Mo T91 martensitic steel
Keller, Clément ULg; Margulies, Monique; Hadjem-Hamouche, Zehoua et al

in Material Science and Engineering A (2010), 527

The tensile behaviour of a modified 9Cr–1Mo T91 martensitic steel is investigated for temperatures between 300 and 700 K. Loading/unloading tensile tests are carried out to investigate the evolution of ... [more ▼]

The tensile behaviour of a modified 9Cr–1Mo T91 martensitic steel is investigated for temperatures between 300 and 700 K. Loading/unloading tensile tests are carried out to investigate the evolution of the tensile flow parameters and the different flow stress components with temperature. An increase in temperature reduces the ductility and the ultimate tensile stress. Three different deformation mechanisms are operative depending on the temperature. These mechanisms are discussed in terms of activation volume, dislocation motion and dynamic strain ageing. [less ▲]

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