Development of an experimental measuring system to be used in bulge test for sheet metal material characterization

Abstract

The success of forming components in sheet metal forming operations is strongly dependent on properties of raw material, being its characterization of great importance to predicting its behavior. A fundamental constitutive modeling of material is the plastic flow curve, relating stress with plastic strain, which is usually based from data obtained in uniaxial tensile testing. However, the limited range of deformation obtained in this test has motivated a growing interest in the bulge test due to its higher levels of attainable deformation. This need is evident when numerical simulation of metal forming processes is performed, because material’s behavior can be described more accurately, with less extrapolation of experimentally obtained data.
This work presents the development and integration of a mechanical measuring system into a hydraulic bulge machine, which allows the continuous data acquisition of pressure, sheet curvature and in-plane strain. With this data, it is possible to obtain the stress-strain curve of the material with higher levels of plastic strains. Results from numerical simulations by finite element analysis are presented and sensitivity studies are used for the definition of some fundamental measurement parameters in order to understand their influence and find their best balance to obtain an accurate flow curve. Additionally, experimental results are presented corresponding to different materials, using and validating the developed experimental system.