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Vers une meilleure compréhension et caractérisation du comportement des aciers à très haute température

Abstract : The understanding of solidification crack phenomena would be a challenge. On the one hand, industrial concerns are considerable, in terms of quality and productivity. On the other hand, this is also a scientific challenge, because the physical mechanisms of hot tearing are far from being understood. One of challenges is the rheological characterization of alloys, which is particularly difficult at high temperature and in the semi-solid state (i.e high temperature and very law strain and strain rate). The rheological characterizations in solid and semi solid state are carried out using a direct resistance heating machines (Taboo). The Taboo set up allows cyclic loadings at very low strain rate (10-3 10-4 s-1) between 900°C and the solidus temperature. A specificity of resistance heating machine is a high non thermal homogeneity on central part of sample; this non thermal homogeneity produces a heterogeneous strain. This heterogeneous strain needs to know the displacement field on the sample. All limits of classical measurement technique bring us to develop a new method based on laser produced speckles and to avoid the high temperature problem. In this work we also present a technique of analysing picture based on a cross spectrum method. We have developed a finite element model able to simulate the entire experimental process. This numerical model, first have permitted to help designing optimal sample geometry in order to minimise the temperature gradients throughout the samples. Then the numerical model is also able to simulate the complete tensile test (including the heating with a temperature control by a PID). The results of tensile test and the numerical simulations are both used in an inverse analysis method to identify mechanical parameters of two different steel grades. Finally we have also explored microscopic phenomenon with a molecular dynamics approach. With a such approach, we have determined solid and liquid thermo mechanical properties of Iron like viscosity, elastic properties. We have also explained the cavity formation.
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Submitted on : Wednesday, August 31, 2011 - 10:40:07 AM
Last modification on : Thursday, September 24, 2020 - 5:22:54 PM
Long-term archiving on: : Thursday, December 1, 2011 - 2:21:36 AM

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  • HAL Id : pastel-00617963, version 1

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Christophe Pradille. Vers une meilleure compréhension et caractérisation du comportement des aciers à très haute température. Matériaux. École Nationale Supérieure des Mines de Paris, 2011. Français. ⟨NNT : 2011ENMP0017⟩. ⟨pastel-00617963⟩

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