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Etude et modélisation des mécanismes d'endommagement en forge à froid

Abstract : The process of cold forging enables to produce parts that exhibit a complex geometry and a very good dimensional accuracy. The final shape is obtained by a forging sequence, and the material is subjected to non-monotonic complex multiaxial loadings together with high plastic strain which can lead to damage: surface or internal cracks initiation. It is consequently very important to get a better understanding of the mechanisms that can produce these defects. The aim of this work thus concerns the numerical modeling of damage growth in cold forging processes. After a literature survey on ductile damage mechanisms and models, the phenomenological Lemaitre damage model has been implemented in the finite element software Forge2005 ®. In a second step, an experimental study on the characterization of two ductile steels was carried out. Different tensile tests were conducted to study the influence of particles orientation on damage growth. Compression / traction tests have also been made in order to examine the possible influence of pre-compression on the material ductility. Finally in situ tests (SEM and X-ray tomography) were conducted to observe and understand microstructural damage mechanisms. Based on these observations, several improvements have been made to make damage computation more suitable to complex loadings. Among these improvements, we can cite a particular formulation to account for damage in compression, the introduction of a negative stress triaxiality limit, the definition of a new damage potential and finally the use of particles orientation to account for damage anisotropy. Finally, numerical simulations have been carried using the Forge2005 ® software in order to validate the new damage model implemented. Validation cases involving simple mechanical tests (tensile, TELE) and industrial cases were then simulated and compared with experimental results.
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Submitted on : Monday, February 1, 2010 - 9:59:00 AM
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  • HAL Id : tel-00451888, version 1

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Ludovic Bourgeon. Etude et modélisation des mécanismes d'endommagement en forge à froid. Mécanique [physics.med-ph]. École Nationale Supérieure des Mines de Paris, 2009. Français. ⟨NNT : 2009ENMP1671⟩. ⟨tel-00451888⟩

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