Effect of the hardening rules on the creep age forming prediction of 7050 aluminum alloy with experimental verification

Abstract

The creep age forming (CAF) has been used in the aerospace sector due to its attractive characteristics that allows producing a component with low residual stress. The process has been studied from the finite-element simulations which are used mainly to predict the springback. However, to accomplish the simulation, it is necessary to set the CAF constitutive equations in the finite-element software. In addition, it is also necessary to define the hardening rule which is applied to determine the creep strain. This work aims to investigate CAF applying the finite-element analysis with the timehardening rule and strain-hardening rule and thus predicting creep strain, stress relaxation, and springback. The finiteelement simulations were accomplished in dies with single and double curvatures and the blank's material was the alloy AA7050. Furthermore, the Marin-Pao model was implemented in the MSC.Marc software through a user subroutine. This model was fitted to the creep experimental curves and it generated good agreement with the experimental data. The results of the simulations that used the time-hardening rule were similar to the strain-hardening rule, and therefore, if it had been chosen a hardening rule, it would not have generated a significant impact in the CAF simulation results. At the end, the simulated springback was compared to the experimental springback from the literature and the percentage error ranged from 0.46% to 15.33% that indicate the proximity with the literature data. Moreover, other experimental validation was performed, and when compared to the results of this methodology, the calculated error in springback was 6.3%.