Investigation of the mechanical behaviour of thin metal sheets using the hydraulic bulge test

A. Diehl, D. Staud, U. Engel
Chair of Manufacturing Technology, University of Erlangen-Nuremberg Egerlandstr. 11, D-91058 Erlangen / Germany

Abstract

Ongoing miniaturisation leads to increasing complexity of micro parts linked with continuously decreasing development time. Hence, the demand for reliable material data and means to collect these data in a most efficient way is rising. Since the mechanical properties and thus material forming behaviour are dependent on the stress and strain conditions, the test methods have to be as close as possible to real conditions. Further, due to the so called size effects, data gathered from conventional length scale experiments cannot be used for the description of material used for parts with feature sizes in the micrometer range. In the present paper, the hydraulic bulge test as a means for the mechanical characterisation of thin metal sheets with thicknesses in the range of 25 μm to 500 μm is discussed and compared to data obtained by conventional tensile testing. Challenges due to the small sheet thickness are emphasized and the effect of strain rate on the flow curve is shown. The influence of geometric dimensions on the evaluation of the experiments is investigated by downscaling of the hydraulic bulge test. The material flow curves, as well as the forming limits are discussed in dependence of the sheet thickness.