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Bandes de cisaillement en thermo-viscoplasticité dynamique : applications à l'usinage et à la rupture ductile des métaux

Abstract : In the first part of this thesis, we investigate the flow through the primary shear zone in orthogonal cutting modeled as a thin band of constant thickness and infinite extend. the viscoplastic flow within the band is analysed in the framework of a one dimensional approach. heat conduction effects and strain-rate sensitivity of the flow pattern are studied. The analysis is then applied to an AISI 4340 steel for which the cutting force and the shear angle are calculated. The calculations are in good agreement with experimental results found in the literature. In the second part, the role of a linear relation between velocity and stress, introduced as a mixed boundary condition, in the non-linear stability of thermo-viscoplastic flows is investigated with the finite element method. Two problems are formulated. First, we consider steady state solutions that are relevant once the strain hardening of the material has satured. Numerical simulations of the time-evolution of the temperature and of the deformation are reported to assess the non-linear stability of the steady states. Typically, two stable steady states act as attractors and the evolving system starting from an unstable steady state selects one of them depending on the perturbation. These attractors and the time required to approach them depend on the mixed boundary condition. The second problem concerns the analysis of the localization process in the kolsky bar experiment. It is shown how the boundary condition affects the shear band thickness and the rate at wich the stress drops. Finally, the results of a dynamic analysis are presented to validate the quasi-static approximation and the assiociated mixed boundary condition
Mots-clés : Métaux-Ductilité
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Laurent Bodin. Bandes de cisaillement en thermo-viscoplasticité dynamique : applications à l'usinage et à la rupture ductile des métaux. Autre. Université Paul Verlaine - Metz, 1996. Français. ⟨NNT : 1996METZ031S⟩. ⟨tel-01777086⟩

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