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Endommagement des aciers TWIP pour application automobile

Abstract : Ultra high strength Fe-Mn-C Twinning Induced Plasticity (TWIP) austenitic steels exhibit excellent formability for automotive safety parts. By refining the microstructure during straining, deformation twinning induces a high hardening rate and provides high ultimate tensile strength (>1000MPa) combined with excellent ductility (>50%). However, plastic instabilities and TWIP effect lead to atypical failures modes and standard forming limit curve based analyses cannot be applied to these materials. In this study, the anisotropic and kinematic plastic flow behaviour of the TWIP steels are evidenced by various mechanical tests. Critical failure parameters are identified for the various testing conditions and compared to mechanical modelling by using numerical simulation of the experimental database. Slant fracture is observed whatever the loading mode, i.e. ductile fracture occurs suddenly without localized necking. Fracture surfaces are characterized by tiny dimples less than 0.5 μm in size. Only little damage is observed underneath the fracture region. Such information concerning macroscopic and microscopic mechanisms leads us to successfully develop phenomenological fracture criterion based on the Barlat91 equivalent stress and Lode parameter (also redefined by considering the Barlat91 model). Influence of hydrostatic pressure and of the Portevin-Le Châtelier effect on the forming limit curve is discussed.
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Submitted on : Friday, April 20, 2012 - 11:07:52 AM
Last modification on : Wednesday, November 17, 2021 - 12:28:18 PM
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  • HAL Id : pastel-00689791, version 1


Julie Lorthios. Endommagement des aciers TWIP pour application automobile. Matériaux. École Nationale Supérieure des Mines de Paris, 2011. Français. ⟨NNT : 2011ENMP0085⟩. ⟨pastel-00689791⟩



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