Etude expérimentale de la fissuration des aciers 40-NCD-16 et XC-18 par impact et usinage rapide : application à l'analyse des déformations par imagerie numérique

Abstract : This study is aimed at analysing the adiabatic shear phenomenon with high strain-rate behaviour. Two materials are studied : a martensitic steel (40-NCD-16) and a medium carbon steel (XC-18). A new experimental device has been designed to generate dynamic load in mode II and to reproduce the orthogonal cutting process at very high speed. This experimental device presents few innovations : (i) the projectile is guided in the launch tube for an optimal precision of the trajectory and to ensure that no rotation of the projectile may occur, (ii) a strain gages set is realised on the Hopkinson tube for the measurement of stress, (iii) numerical images of tests are given by a system made up CDD rapid cameras. The adiabatic shear band (ASB) obtained onto 40-NCD-16 prenotched plate are quite surprising. They are initiate on the impact face and propagate to the upper and lower side of the specimen. The results found in literature gives a propagation in the notch continuation. Tests on other germany plate of XC18 give three different breaking modes as a function of impact rate. A critical rate corresponding with a breaking ASB is defined. A microscopic analysis of deformation, with a numerical image study method near the impact zone, give the results on dimensional and deformation of grains. The phenomenon of localisation can also be connected with microstructural mechanism (elongation and rotation of grains). The effects of the very high cutting speed on the chip segmentation are lastly studied. The results obtained show that the evolution of the cutting force, in terms of rake angle and cutting velocities, can be correlated to morphological aspects. The cutting force are decreasing with the occurence of the shear banding
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Laurent Faure. Etude expérimentale de la fissuration des aciers 40-NCD-16 et XC-18 par impact et usinage rapide : application à l'analyse des déformations par imagerie numérique. Autre. Université Paul Verlaine - Metz, 1997. Français. ⟨NNT : 1997METZ052S⟩. ⟨tel-01777231⟩

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