Comparison of the strain-hardening parameters of sheet metals in uniaxial and biaxial tension

Abstract

The strain-hardening parameters of steel, copper and brass were determined by uniaxial and balanced biaxial tensile tests. The stress-strain relationship of steel was well described by the Hollomon equation while, the Voce equation was valid for copper and brass. Thus the use of then-value as a measure of strain-hardening ability is justified for steel only and uniform strains have to be used for copper and brass. The uniaxial and biaxialn-values of steel were found to be equivalent. However, the stress-strain relationships of copper and especially brass were observed to be stress-state dependent. Forming limit diagrams of the materials were constructed using hydraulic bulging and tensile tests. The FLDs were also calculated using the plastic instability conditions and the strain-hardening parameters determined.