Accurate determination of biaxial stress-strain relationships from hydraulic bulging tests of sheet metals

The meridional strain gradient in hydraulic bulging of sheet metal through a circular aperture is severe. The resulting thickness gradation affects the bulge shape and complicates the evaluation of representative strain and stress at the pole of the bulge. An earlier solution for calculation of polar strain is extended to provide accurate explicit formulations of the thickness variation and the effective radius of curvature near the pole of the bulge. The representative stress-strain relationship determined for the biaxial stress state at the pole is shown to be significantly affected by these corrections. (C) 1997 Elsevier Science Ltd. All rights reserved.