Unbalanced - biaxial stretching with a hydraulic bulging equipment

Abstract

These are diagrams showing the limit strains or deformations which can be borne by steel plates on their plane when they are formed. The limits here indicated are in correspondence with the different capabilities for stamping shown by each material. These diagrams are known as Forming limit diagrams (FLD). For the preparation of these (by tests), different strain paths are reproduced enabling data acquisition. The Metallurgy Laboratory of the U.N.S. has an hydraulic cupping equipment originally designed to obtain a balanced biaxial traction of a test-piece. For this, a mask with a circular opening is used. It is possible to reproduce the strain paths located on the right quadrant of the before-mentioned diagram by tests with hydraulic cupping (both positive strains), that is, balanced and non-balanced biaxial traction. This paper proposes to adapt this equipment for the obtention of non-balanced biaxial traction paths. In order to achieve this goal, masks with an elliptical opening are designed for the fixing of the test piece. The strain path therefore depends on the half axles of the ellipse. As with the first mask´s design, the test piece was deformed outside the ellipse´s area, its anchorage system was modified so that the deformation remains within the area of the elliptical opening.