Comportement des métaux multiphasés sous sollicitations dynamiques.prise en compte des transformations métallugiques.

Abstract

The present work deals with the experimental and numerical study of cylindrical slugs and thin tubes in stainless steel (AISI 304L) in quasi-static and dynamic (impact) regime taking into account the martensitic transformation. An exhaustive bibliographical research was carried out on stainless steels with TRIP effect, thermodynamics of the martensitic transformation and numerical models taking into account the effect of the deformation rate and the kinetics of the transformation. A battery of experimental tests were carried out: axial compression tests in quasi-static and dynamic regime at different deformation rates. Metallurgical and magnetic characterisations (SEM, XRD, VSM, microhardness and hardness) were conducted on specimens before and after deformation. The creation of martensite in the specimens after deformation was demonstrated. Quantification of the martensite fraction was realised with ImageJ software on micrographic captures. A decrease in the amount of martensite formed with increasing strain rate was detected. The viscoplastic Abedvoyadjis model in the case of CFC and CC was combined with the transformation kinetics. The extended model was then implemented in the Abaqus/Explicit finite element code using the VUMAT subroutine. The proposed numerical model was validated on a volume element. Thereafter a parametric study was launched to calibrate and estimate the effect of each parameter on the macroscopic behaviour of the steel investigated. Another study was also conducted on the effect of the mesh size on the numerical response of the implemented model. Numerical simulations were performed on slugs and tubes at different strain rates in the quasi-static condition. The proposed model accuratelyreproduces the experimental data.