A pure bending machine to identify the mechanical behaviour of thin sheets
Résumé
It is now commonly accepted that the so-called Baushinger effect has to be taken into account for accurate springback predictions during sheet metal forming simulations. Baushinger effect can be modelled through the introduction of a kinematic hardening law in the material model. The identification of such a behaviour requires to perform tests such that the material is subjected to reversal loadings. In the case of thin sheets, tension-compression tests are impossible because of buckling. Two alternative solutions can be found in the literature: shear tests and bending tests. Since bending tests are more representative of the behaviour of the material during many industrial metal forming processes, several authors have recently proposed bending machines for such applications. This paper is devoted to the presentation of an original pure bending machine developed at LMT-Cachan (patent pending 2002). The machine architecture and kinematics is presented. It enables to bend specimens up to 90° (i.e. 13% strain at the surface of a 1 mm thick and 6 mm long specimen). The bending moment is simultaneously applied to two identical specimens so that no spurious "normal" and "shear" loads are applied to the specimens as experimentally verified through the measurement of moments in different points of the machine. Strain fields can be obtained directly from strain gauges glued on the specimens or from the motors angle and the compliance of the machine. The capabilities of this original pure bending machine are illustrated herein by tests performed on different materials including a 0.25 mm thick TRIP steel sheet.
Origine : Fichiers produits par l'(les) auteur(s)
Loading...
