The effect of height to diameter ratio at stack compression tests on biaxial yield stress

Abstract. This study presents experimental stack compression test results of samples with different height-to-diameter (aspect) ratios for a simplified calculation of the friction- and the stress state contribution on the flow stress compared to the case of simple tension. Standard uniaxial tension tests formed the basis of the investigations as reference curves, and the stack compression tests were carried out on the same material, on commercially available DC04 steel sheet. The aim was to experimentally observe and possibly separate the anisotropic, pure material behavior from the friction-forced reaction of the material to determine the equi-biaxial yield stress for proper yield surface election. Our results show that with proper lubrication conditions, the stress increase caused by friction can be kept at low value for high aspect ratios, as well as with the comparison of the high and low aspect ratios, the value of the Coulomb friction coefficient, and thus the friction contribution on the flow stress can be calculated. After a stress compensation based on the obtained friction coefficient, the calculated stress ratios led to the monitoring of the goodness of different yield surfaces.