Mechanical Behavior and Microstructural Development of Low-Carbon Steel and Microcomposite Steel Reinforcement Bars Deformed under Quasi-Static and Dynamic Shear Loading

Reinforcement bars of microcomposite (MC) steel, composed of lath martensite and minor amounts of retained austenite, possess improved strength and corrosion characteristics over low-carbon (LC) steel rebar; however, their performance under shear loading has not previously been investigated at the microstructural level. In this study, LC and MC steel cylinders were compression tested, and specimens machined into a forced-shear geometry were subjected to quasi-static and dynamic shear loading to determine their shear behavior as a function of the strain and strain rate. The as-received and sheared microstructures were examined using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Higher-resolution microstructural examinations were performed using transmission electron microscopy (TEM). The influence of the starting microstructure on the shear behavior was found to depend strongly on the strain rate; the MC steel exhibited not only greater strain-rate sensitivity than the LC steel but also a greater resistance to shear localization with load. In both steels, despite differences in the starting microstructure, post-mortem observations were consistent with a continuous mechanism operating within adiabatic shear bands (ASBs), in which subgrains rotated into highly misoriented grains containing a high density of dislocations

Dynamic recrystallization : classical concepts and new aspects.

International audienc

Claude Rossard, pionnier français de l'étude des traitements thermomécaniques.

National audienc

Mise en oeuvre des alliages de titane par déformation plastique.

National audienc

INFLUENCE OF FLOW RULE AND INERTIA ON VOID GROWTH IN A RATE SENSITIVE MATERIAL

La déformation d'une cavité ellipsoïdale de révolution dans une matrice infinie soumise à une sollicitation dynamique est étudiée. On montre l'effet stabilisant sur la croissance de l'endommagement de la vitesse de traction et des effets d'inertie dans le domaine dynamique ([MATH]).The growth and deformation of a spheroidal void in an infinite viscous matrix is addressed. In the case of a linearly viscous (newtonian) matrix ([MATH]), an exact solution is obtained. On the basis of this solution the case of a power law viscoplastic matrix ([MATH]) is dealt with by a variational approach. Finally, the Galerkine method is used to take into account inertia effects. This work shows the anisotropy of damage and the stabilizing effect of the remote strain rate [MATH] for a material exhibiting the linear flow rule [MATH] as well as the stabilizing effect of the inertia forces

Recristallisation Continue au Cours de la Déformation à Chaud d'un Aluminium 1200

La recristallisation dynamique continue se manifeste par la transformation progressive des sous-grains en grains. Une étude microstructurale effectuée par diffraction des électrons rétrodiffusés a permis de la mettre en évidence lors de la déformation par compression uniaxiale (0,7 Tf, 10-2 s-1) d'un aluminium 1200 (99,3 %).Continuous dynamic recrystallization is characterized by the progressive transformation of the subgrains into grains. This process was investigated by electron back scattered diffraction during uniaxial compression (0,7 Tf, 10-2 s-1) of a 1200 aluminium (99,3 %)