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Contribution micromécanique au comportement multi-échelles d'un matériau composite élastoplastique lamellaire : Application à l'étude des effets du recyclage sur la tréfilabilité d'un acier perlitique industriel

Abstract : Pearlitic steel cords may reach a tensile strength up to 4 GPa and still exhibit some ductility. This unusual property (close to wiskers strength) is related to the process of cold drawing which reduces the size ? [lambda] of the lamellar substructure, in proportion to the wire diameter (Embury's similitude principle) and induces the formation of crystalline and morphological textures : the single crystal lamellae behave elastoplastically. Usually, the draw hardening is theoretically explained in terms of the combination of a macroscopic Hall-Petch law in ? [exposant] -½ , with the similitude principle applied to wire drawing. In the case studied, the initial size of the substructure (some 10 nm) does not allow a dislocation's pile-up mechanism. However, the experimental draw hardening exhhibit a slope (In(Rm) = k ?drawing) with k=1/4, which is consitent with a macroscopic Hall-Petch law of type kH.P.? -½ .Using a scale transition method based on a non pile-up model for dislocations, the theory proposed here aimed to model the draw hardening of lamellar pearlitic steel. The reduction of the dislocation's mean free path in proportion to the lamellar spacing ? is the main factor studied here, taking no account of the cristalline textures developped during wire drawing. This simple method for calculating the draw hardening curve results in a slope of value ¼ , which is the experimental one's. Thus, a draw hardening slope of 1/4 does not mean a dislocation's pile-up mechanism at the microscale. In other words, the averaging process used to relate the macroscopic strength to the size and the history evolution of the microstructure needs refinements as proposed in this model
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Raphaëlle Krummeich. Contribution micromécanique au comportement multi-échelles d'un matériau composite élastoplastique lamellaire : Application à l'étude des effets du recyclage sur la tréfilabilité d'un acier perlitique industriel. Autre. Université Paul Verlaine - Metz, 2001. Français. ⟨NNT : 2001METZ040S⟩. ⟨tel-01748969⟩

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