Analytical methodology for the determination of the flow curves of aluminum and steel alloys using the hydraulic bulge tests

In sheet metal forming simulation, flow curve is a vital ingredient for reliable numerical results. It is more appropriate to determine the flow curve using biaxial stress state tests such as hydraulic bulge test instead of uniaxial test because hardening proceeds to higher strains. With a uniaxial test, higher strains are extrapolated which might lead to incorrect results. The bulge test coupled with the digital image correlation (DIC) system is utilized for the determination of the stress-strain data. In the absence of DIC system, analytical methodologies were used to estimate hardening. Typically such models incorporate a correction factor to achieve correlation to experimental data. An example is the Chakrabarty and Alexander method which uses a correction factor based on the n-value. Here, the Chakrabarty and Alexander approach is modified by utilizing a correction factor based on normal anisotropy. When compared to DIC data, the modified model was found to be predictive of hardening curves for the materials under this study.