Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 54 4 2022 06 22 Investigation on the Effect of Different Constitutive Models on the Forming Limit of the Sheet under Nonlinear Strain Path Investigation on the Effect of Different Constitutive Models on the Forming Limit of the Sheet under Nonlinear Strain Path 925 944 4714 10.22060/mej.2022.20519.7256 FA Soheila Sojodi Faculty of Mechanical Engineering, University of Guilan Ali Basti Faculty of Mechanical Engineering, University of Guilan, Rasht, Iran Seyed Reza Falahatgar Faculty of Mechanical Engineering, University of Guilan, Rasht, Iran 0000-0003-1573-5619 Seyedeh Maryam Mirfalah Nasiri Faculty of Mechanical Engineering, University of Guilan Journal Article 2021 09 12 Forming limit diagrams are a criterion to predict the necking for constructing an optimal design in metal products. In this paper, the Marciniak-Kuczynski instability theory is used to determine the forming limits of the AA6111-T43 sheet. Also, Hill 48, Gotoh, and Yld2000-2d yield criteria are investigated to describe the yield behavior of the alloy, and their coefficients are computed based on the results obtained from uniaxial and bulge tests. Finally, forming limit diagrams are plotted by employing different yield functions and appropriate hardening models. The comparison between theoretical and experimental results indicated that the limit strains obtained by the Yld2000-2d criterion and Swift model are in better agreement with experimental data than others. Since in complex forming processes, the strain path is rarely linear, the investigation of the forming limit diagram by considering the nonlinear strain path is important. In multi-stage forming processes, while the limit strains are significantly path dependent, the forming limit stress diagram is less dependent on the loading path. However the sensitivity of the forming limit stresses to the path is lower than limit strains, the limit stresses in large pre-strain are not completely loading path independent. The sensitivity of the limit stresses to strain path in addition to the magnitude of the pre-strain, also depends on the used hardening model and yield function that are examined in detail in this study. Forming limit diagrams are a criterion to predict the necking for constructing an optimal design in metal products. In this paper, the Marciniak-Kuczynski instability theory is used to determine the forming limits of the AA6111-T43 sheet. Also, Hill 48, Gotoh, and Yld2000-2d yield criteria are investigated to describe the yield behavior of the alloy, and their coefficients are computed based on the results obtained from uniaxial and bulge tests. Finally, forming limit diagrams are plotted by employing different yield functions and appropriate hardening models. The comparison between theoretical and experimental results indicated that the limit strains obtained by the Yld2000-2d criterion and Swift model are in better agreement with experimental data than others. Since in complex forming processes, the strain path is rarely linear, the investigation of the forming limit diagram by considering the nonlinear strain path is important. In multi-stage forming processes, while the limit strains are significantly path dependent, the forming limit stress diagram is less dependent on the loading path. However the sensitivity of the forming limit stresses to the path is lower than limit strains, the limit stresses in large pre-strain are not completely loading path independent. The sensitivity of the limit stresses to strain path in addition to the magnitude of the pre-strain, also depends on the used hardening model and yield function that are examined in detail in this study. https://mej.aut.ac.ir/article_4714_cb59b747f88a35e0d452377f60f7c25f.pdf