Development of a Hydraulic Bulge Test to Determine the Work Hardening Behaviour of Sheet Materials

The objective of this research is to develop an experimental facility that is able to characterize the work hardening behaviour of metal sheets up to large deformations greater than 50 percent effective strain. A hydraulic bulge test die was designed with a 120-mm diameter piston to push the forming fluid against the sheet specimen, a 135-mm diameter opening and a 3-mm radius on the fillet of the die. This die was built and installed in a double-action hydraulic press and is capable of reaching a forming pressure of 60 MPa. DP600 steel sheet specimens were also flat rolled to effective strains of 0.2, 0.4, 0.6, 0.8 and 1.0 and tensile tests were conducted on the as-rolled specimens following ASTM E8 standards. A power law curve was fitted to the data, and yielded ̅=1026.851 ̅ 0.1951 in the rolling direction and ̅=1022.456 ̅ 0.1758 in the transverse direction. Hydraulic bulge tests were successfully run and the experimental data was fitted to ̅=1104.6 ̅ 0.2029. Finite element (FE) models of the hydraulic bulge test and uniaxial tensile test were constructed. FE models were validated using an appropriate validation metric, and the predicted uniaxial tension flow curve showed a validation score of 0.97 and the flow curve predicted for the hydraulic bulge test achieved a score of 0.98, compared to the experimental curves. Power law, Ludwik and Voce functions were fitted to the experimental data and hardening parameters were determined for both the tensile test with successive flat rolling and the hydraulic bulge test flow curves. Comparison metrics were established at 0.94, 0.87 and 0.94, respectively. Comparisons were made between the tensile test flow curve and the hydraulic bulge test flow curve which showed that the hydraulic bulge test is better suited for the characterization of work hardening behaviour up to large strains