In this work, yield surfaces were measured for binary aluminum-magnesium sheet samples which were fabricated by different processing paths to obtain different microstructures. The yielding behavior was measured using biaxial compression tests on cubic specimens made from laminated sheet samples. The yield surfaces were also predicted from a polycrystal model using crystallographic texture data as input and from a phenomenological yield function usually suitable for polycrystalline materials. The experimental yield surfaces were found to be in good agreement with the polycrystal predictions for all materials and with the phenomenological predictions for most materials. However, for samples processed with high cold rolling reduction prior to solution heat treatment, a significant difference was observed between the phenomenological and the experimental yield surfaces in the pure shear region. In this paper, a generalized phenomenological yield description is proposed to account for the behavior of the solute strengthened aluminum alloy sheets studied in this work. It is subsequently shown that this yield function is suitable for the description of the plastic behavior of any aluminum alloy sheet.

Yield function development for aluminum alloy sheets

Crystallographic texture, anisotropic yield surfaces and forming limits of sheet metals

This paper presents synthetically the most recent models for description of the anisotropic plastic behavior. The first section gives an overview of the classical models. Further, the discussion is focused on the anisotropic formulations developed on the basis of the theories of linear transformations and tensor representations, respectively. Those models are applied to different types of materials: body centered, faced centered and hexagonal-close packed metals. A brief review of the experimental methods used for characterizing and modeling the anisotropic plastic behavior of metallic sheets and tubes under biaxial loading is presented together with the models and methods developed for predicting and establishing the limit strains. The capabilities of some commercial programs specially designed for the computation of forming limit curves (FLC) are also analyzed.

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Advances in anisotropy and formability

The development of surface roughening during uniaxial tensile deformation, with particular attention to the development of parallel ridges and valleys (ribbed profile), has been investigated for a commercial aluminium alloy. A comparison has been made between two samples which exhibit different propensities for roughening and a detailed microstructural characterisation of these samples has been performed in order to explain the differences. Microstructural characterisation techniques included polarised light microscopy, bulk texture and microtexture. In addition, yield properties were calculated from the microtexture data using polycrystal plasticity analysis. The results show that the differences in the roughening behaviour can be attributed to spatial differences in texture at the specimen surface whereby R-component colonies in a cube matrix produce differential straining, which eventually leads to strain localisation through the specimen thickness to produce a ribbed profile.

P. Bate

Papers

The prediction of limit strains in steel sheet using a discrete slip plasticity model

Strain localisation in biaxially stretched sheets containing compact defects—II: Analysis using a finite element model