Effect of plastic anisotropy on shear localization and fracture in automotive sheets

Tensile instability, as characterized by the Considère law, is one of the factors governing formability of metallic sheets. During tensile deformation, material thins in a narrow band due to shear localization, prior to final fracture. Strain rate value within the localized necking band tends to be higher than outside it and final fracture is governed both by the nature of the shear localization as well as the strain rate differential between the neck and the material outside the neck. This paper reports the dependence of shear localization and fracture on plastic anisotropy of the material. Three types of automotive sheet materials, namely IF steel (BCC structure), AA5754 aluminum alloy (FCC) and AZ31 magnesium alloy (HCP) are examined. Digital image correlation is used to follow the development of deformation pattern during tensile tests. The results show that both narrowing and thinning of the tensile sample occur in IF steel, while only thinning occurs in AA5754 and only narrowing occurs in AZ31. These differences arise from the differences in the plastic anisotropy of the three materials, as measured by their r-values. Even though all three materials exhibit ductile fracture, the damage and fracture processes in the three materials differ from each other. Copyright © (2013) by International Conference on Fracture.