Plastic instabilities in AA5754-O under various stress states

Abstract

Spatio-temporal characteristics of plastic instabilities in the aluminium alloy sheet AA5754-O were investigated under three different stress states: uniaxial tension, plane strain and equi-biaxial tension. Tensile tests including conventional uniaxial tensile specimens as well as optimized ISO 16842 cruciform specimens for plane strain and equi-biaxial tensile deformation conditions were carried out at room temperature. Arm strength of the cruciform specimens was enhanced by laser deposition of thickening layers using Al-Mg alloy wire material in order to delay fracture and extend the equivalent plastic strain in the gauge area of the cruciform specimens from ~0.03 to ~0.13 under plane strain condition and to ~0.07 under equi-biaxial tension. The differences in serrated flow behaviour and spatio-temporal evolution of Portevin–Le Châtelier (PLC) bands under these three stress states were investigated using digital image correlation (DIC) techniques. The originality of this paper is to present different PLC phenomena under plane strain condition and equi-biaxial tension, which requires improved models or modifications of existing theoretical frameworks for uniaxial tension to account for different characteristics of PLC phenomena under plane strain and equi-biaxial tension of Al-Mg alloy sheets.