Caractérisation et modélisation multi-échelles de l’anisotropie et de l’hétérogénéité de la déformation plastique du alpha-titane en conditions de traction

Abstract : The plasticity of alpha-titanium is strongly anisotropic. It involves slip systems families with various properties and different kinds of twins. In this study, tensile tests on commercially pur alpha-titanium samples are coupled with acoustic emission and high-resolution extensometry measurements. These tests show the presence of a well on the strain dependence of the work hardening. An opposite strain rate effect on the well depth is found whether specimens are elongated along the rolling or the transverse direction of the initially laminated sheet. Slip lines analysis reveals an initial predominance of prismatic slip, particularly pronounced in specimens strained along the rolling direction. The relative activity of prismatic slip is then observed to decrease with the deformation of both kinds of samples. The twin volume fractions are higher in the tests performed in the transverse direction but still remain very low (< 5 %), especially around the well (< 2 %). These results provide grounds for elaboration of a model capable of explaining such peculiar work hardening behavior. The model relies on a self-consistent scheme in elastoviscoplasticity, based on the translated field method and an affine linearization of the viscoplastic flow rule. The model considers crystal plasticity and deals separately with mobile dislocation density and dislocation velocity. It assumes lower strain rate sensitivity as well as higher dislocation multiplication rate for prismatic systems. Based on these assumptions, the model reproduces correctly the stress-strain curves and gives sound estimates of Lankford coefficients, prismatic slip activity and textures evolution. Most importantly, the opposite effect of strain rate on the well depth with regard to the orientation of the tensile axis is qualitatively retrieved, which allows putting forward an explanation of the observed phenomena. Besides, acoustic emission and high-resolution extensometry measurements allow analyzing the intermittent and wave nature of alpha-titanium at a mesoscopic scale. These data are confronted with the predictions of the present model and will be used as grounds for the future development of a more complex model
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Eva Kékéli Amouzou. Caractérisation et modélisation multi-échelles de l’anisotropie et de l’hétérogénéité de la déformation plastique du alpha-titane en conditions de traction. Autre [cond-mat.other]. Université de Lorraine, 2015. Français. ⟨NNT : 2015LORR0200⟩. ⟨tel-01754460⟩

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