Dominique Daniel

Estimation of 4th and 6th Order ODF Coefficients From Elastic Properties in Cold Rolled Steel Sheets

Generally only the 4th order ODF coefficients are deduced from the observed elastic anisotropy of textured polycrystalline materials with cubic/orthorhombic symmetry. In this study, a method is described for the prediction of the 4th and 6th order ODF coefficients from the elastic properties of cold rolled and annealed steel sheets of 5 different types. In order to link these properties with the texture, the elastic energy method of Bunge (1974) is employed. By estimating the volume fractions of the principal preferred orientations and their gaussian spreads, ODF coefficients of the 4th (C411, C412 and C413) and 6th (C611, C612 and C614) orders can be successfully obtained. As a result, the planar r-value distribution can be predicted more accurately than when only the 4th order coefficients are employed.

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.

ESTIMATION OF 8th, 10th AND 12th ORDER ODF COEFFICIENTS FROM ELASTIC PROPERTIES IN COLD ROLLED STEEL SHEETS BY ADJUSTMENT OF SINGLE CRYSTAL ELASTIC CONSTANTS

In an earlier paper (Sakata et al., 1989), it was shown that the 4th and 6th order ODF coefficients could be successfully derived from Youngs modulus measurements using the elastic energy method. However, the values of some of the coefficients fell beyond the expected error ranges. In this study, more appropriate single crystal elastic constants are selected by means of a fitting procedure. Then the ODF coefficients are again estimated in the manner described previously. As a result, the values of the C411, C611, C612 and C614 coeffioents, which were somewhat inaccurate in the previous calculation, are improved considerably. The volume fractions of the principal preferred orientations are then employed to predict the 8th order coefficients and the fiber components of the l = 10 and l = 12 (C1011, C1211 and C1221) coefficients. With the aid of the coefficients obtained in this way, both pole and inverse pole figures are drawn, which are in better agreement with those based on X-rays than when only the 4th order coefficients are employed.

Texture Based Finite Element Simulation of a Two-Step Can Forming Process

Aluminum sheets used for beverage cans show a significant anisotropic plastic material behavior in sheet metal forming operations. In a deep drawing process of cups this anisotropy leads to a non-uniform height, i.e., an earing profile. The prediction of this earing profiles is important for the optimization of the forming process. In most cases the earing behavior cannot be predicted precisely based on phenomenological material models. In the presented work a micromechanical, texture-based model is used to simulate the first two steps (cupping and redrawing) of a can forming process. The predictions of the earing profile after each step are compared to experimental data. The mechanical modeling is done with a large strain elastic visco-plastic crystal plasticity material model with Norton type flow rule for each crystal. The response of the polycrystal is approximated by a Taylor type homogenization scheme. The simulations are carried out in the framework of the finite element method. The shape of the earing profile from the finite element simulation is compared to experimental profiles.

The Elastic Strain Ratio, the Lüders Strain Ratio and theEvolution of r-Value During Tensile Deformation

The elastic counterpart of the plastic strain ratio is derived from ultrasonic data measured on twenty commercial deep drawing steels. It is shown that the observed variations in plastic r are related to the evolution of texture, and are not affected either by the elastic range of deformation or by the propagation of Luders bands. Further quantitative analysis suggests that the elastic strain ratio, determined non-destructively, can be used to predict plastic r-values by means of an empirical relationship.

Formability Prediction Of Aluminum Sheet In Automotive Applications

In the following paper, a full mechanical characterization of the AA6016 T4 aluminum alloy car body sheet DR100 is presented. A comprehensive experimental program was performed to identify and model the orthotopic elasto‐plastic deformation behavior of the material and its fracture characteristics including criteria for localized necking, ductile fracture and shear fracture. The commercial software package MF GenYld + CrachFEM in combination with the explicit finite element code Ls‐Dyna is used to validate the quality of the material model with experiments, namely, prediction of the FLD, deep drawing with a cross‐shaped punch and finally, analysis of a simplified hemming process using a solid discretization of the problem. The focus is on the correct prediction of the limits of the material in such processes.

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.