Gilles Guiglionda

Behavior of X-ray peak widths in the Wilkens model of a restractedly random distribution of dislocations: Dedicated to Professor Dr. Haël Mughrabi on the occasion of his 65th birthday

Abstract The behavior of the width of X-ray Bragg peaks recorded froe dislocated crystals has been investigated both numeracally and experimentally. Numerical simulations based on the Wilkens model...

Overview of Forming and Formability Issues for High Volume Aluminium Car Body Panels

Cost-efficient designs of aluminum autobody structures consist mainly of stampings using conventional technology. Progress in metallurgy and forming processes has enabled aluminum body panels to achieve significant market share, particularly for hoods. Fast bake hardening alloys with better hemming performance were developed for improved outer panel sheet products. Specific guidelines for handling and press working were established to form aluminum panels using similar schedules and production lines as steel parts. Stamping productivity was improved by optimization of the trimming process to reduce sliver/particle generation and resulting end-of-line manual rework. Both hemming formability and trimming quality not only depend on tooling setup but also on microstructural features, which govern intrinsic alloy ductility. Targets for the next high volume aluminum car body applications, such as roof panels and doors, require higher strength and/or better formability. The challenges of complex stampings can be met with optimized alloys and lubricants, with improved numerical simulation to fine-tune stamping process parameters, and with the introduction of new technologies. Warm forming was examined as a potential breakthrough technology for high volume stamping of complex geometries.

A Rapid Deformation Texture Model Incorporating Grain Interactions: Application to Aluminium Hot Rolling Textures

A simple and general new approach to predict deformation texture evolution during large plastic strains is presented. The stress in each grain, first calculated by a Taylor model, is then modified by the stresses of adjacent grains thereby making the local slip systems and lattice rotations neighbour dependent. Examples of texture simulations during hot rolling of aluminium alloys are given. The model predictions are compared with the standard Taylor model predictions and with ODF data of the textures measured during hot plane strain compression.

Fundamentals of Bending AA6xxx Sheet

This paper describes recent experimental results on the strain distributions developed during bending of AA6xxx sheet for automotive applications, together with a new model for the mechanics and metallurgy of strain localization during bending. A detailed microscopic study (optical and SEM/EBSD) shows that damage development during bending to strains of order unity is controlled by through-thickness shear banding at the grain scale. A new finite element microstructure-based model is introduced to predict this strain localization during practical bending. The sheet metal is modelled as a grain aggregate, each grain having its own flow stress. After validation, the model is applied to the experimental results through an analysis of the critical plastic strain at the outer surface during bending of AA6016 sheet alloys. It correctly describes the respective influences of sheet thickness, grain size and shape, and work hardening. In particular the model brings out the primary importance of large-strain hardening and the spread of the flow stress distribution.

Characterization of Damage Mechanisms during Bending of 6xxx Aluminium Automotive Sheets

Bendability is a key property of aluminum automotive panels. Previous work showed that the bendability may not be characterized by macroscopic parameters. In the present work, the kinetics of damage development during bending of 6016 sheet was first characterized experimentally. Then, a mechanical model analyzing independently the influence of the microstructure, the flow stress distribution, the hardening behavior of the material and the sheet thickness on the bendability was developed.