Strain Rate-dependent Flow Stress Curves in the Large Deformation Range

This paper deals with the construction method of the flow stress curve at various strain rates in the large deformation range. The hydraulic bulge test is carried out for EDDQ and 590DP steel sheets in order to obtain equi-biaxial flow stress curves according to the punch speed. By using the measured curves, the stress data at various plastic strains is fitted by Cowper-Symonds model in order to analyze the strain rate sensitivity and determine the stress value at the designated strain rate. Equi-biaxial flow stress curves at various strain rates are constructed by fitting the determined stress value with Swift model with respect to the plastic strain. Finally, equi-biaxial flow stress curves are converted into uniaxial flow stress curves by using Yld2000-2d yield function. A suggested procedure can be utilized to construct the uniaxial flow stress curves at various strain rates in the large deformation range.