FE simulation of asymmetric creep-ageing behaviour of AA2050 and its application to creep age forming

A finite element (FE) model has been developed and validated in this study for the first-time to simulate the asymmetric creep-ageing behaviour of an Al–Cu–Li alloy (AA2050) for creep age forming (CAF) applications. An implicit integration algorithm integrated with the Secant method was proposed to efficiently solve the creep-ageing constitutive model of AA2050 and a “maximum principal stress” technique was employed to characterise the asymmetric tension and compression creep behaviour for CAF FE simulation. The proposed algorithm has been implemented into the FE solver in PAM-STAMP via a user-defined subroutine and an implicit FE model has been developed for CAF of AA2050. The effectiveness of the developed FE model has been validated by four-point-bending creep-ageing experiments of AA2050 plates with different thicknesses. The springback behaviour of AA2050 plates after 18 h CAF with a doubly curved tool was then predicted using the validated FE model. The results show that springback levels of the CAFed plates decreased with increasing thickness. Significant springback was observed in all the CAFed AA2050 plates within elastic loading, for example, the 8 mm plate which was initially loaded to near yielding had a springback value of 87.1% after 18 h CAF at 155 °C. The implicit algorithm and the maximum principal stress technique can be employed for constitutive models for other alloys with asymmetric creep-ageing behaviour.