Evaluation of flow stress and damage index at large plastic strain by simulating tensile test of Al6061 plates with various grain sizes

• Methodology for determining flow stress at large plastic strain was provided.
• Methodology for determining damage index at large plastic strain was provided.
• Grain size effect of aluminum plate on flow stress and damage index was investigated.

This work was focused on evaluation of the more accurate flow stresses and damage indices after onset of necking by simulating tensile tests of Al6061 plates with various grain sizes. By assuming strength coefficient and strain hardening coefficient, load vs. displacement curve was obtained from finite element simulation and then was compared with that obtained from the experimental tensile test. By means of repetition of this procedure, the flow stress curve with the accurate strength coefficient and strain hardening coefficient after onset of necking were determined when the error between load vs. displacement curves obtained from simulation and experiment of tensile test was minimized. Through comparison of the deformed shapes obtained from FE simulation and experiment of tensile test, the reliability of flow stress was verified. Based on the flow stress determined, the damage index of normalized Cockcroft–Latham ductile fracture criterion was evaluated at the displacement where fracture initiates during tensile test. Finally, grain size effect of Al6061 plate on the flow stress and damage index was investigated. It was revealed from this work that the strain hardening exponent and damage index increase when the grain size increases. On the contrary, strength coefficient is not so much different regardless of the grain size.