Bandes de cisaillement adiabatique : effets géométriques et effets de conduction

Abstract : Abiabatic shear bands are narrow zones where an intense shear is localized in viscoplastic materials. They result from an instability of the plastic flow, promoted usually by the material thermal softening. The attention is focused on the influence of the sample geometrical and structural defects and of the thermal diffusivity in the final stages of the localization through a one-dimensional model. Asymptotic structural localization criteria are obtained from an abiabatic quasi-static model ; they reveal that the material properties are coupled with the defects shape. The stabilizing influence of rate-sensitivity appears to be enhanced by smooth defects. It is shown that the sharpness and the amplitude of the local defects may help understand the observed scatter in the nominal failure deformation. During the stress collapse, thermal diffusivity effects induce a stabilization and a homogenization of the plastic deformation, they are taken into account in a quasi-static model designed for the study of the band structuration. The observed stabilization of the bandwidth leads to assuming the existence of a steady flow ; though the stationary solutions are found to be unstable in the mechanical conditions of the torsional Kolsky bar test. Therefore an improvement of the stationary hypothesis is proposed by only assuming a steady strain rate distribution. The stress relaxation time is then related to the bandwidth. The model includes the singular material defects and it reveals that the bandwidth decreases as the defect becomes more acute, but that it remains finite for a singular defect
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Florence Dinzart. Bandes de cisaillement adiabatique : effets géométriques et effets de conduction. Autre. Université Paul Verlaine - Metz, 1994. Français. ⟨NNT : 1994METZ005S⟩. ⟨tel-01776035⟩

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