A biaxial test for rheological and formability identification

Université Européenne de Bretagne, INSA-LGCGM - EA3913, 20 avenue des Buttes de Coësmes, CS 70 839, 35708 Rennes Cédex 7, France

^a e-mail: dominique.guines@insa-rennes.fr

Abstract

Accurate constitutive laws and formability limits of materials are essential for a numerical optimization of sheet forming processes. The main objective of this work is to develop a new experimental device able to give for a unique specimen a good prediction of rheological parameters and formability under conditions (low and intermediate strain rates) close to the ones met in processes. The proposed device is a servo-hydraulic testing machine provided with four independent dynamic actuators allowing biaxial tensile tests on a dedicated specimen. By localizing necking in the central zone of the specimen, the strain path in this zone is controlled by the speed ratio between the two axes and the whole forming limit curve can be covered. Such a specimen is proposed throngh a numerical and experimental validation procedure. Finally, an experimental forming limit curve for the aluminium alloy AA5086 is determined thanks to a rigorous procedure for detecting the onset of necking in the specimen.