On the plastic flow rule formulation in anisotropic yielding aluminium alloys

Abstract

In the last decade, an increasing trend has been observed in the use of advanced anisotropic material models to improve the numerical predictions about sheet metal-forming processes. Among the actions following this trend, the use of non-associated flow rule (NAFR) models has been presented as an alternative to the classic associated flow rule (AFR) models. In this work, the influence of the flow rule in advanced anisotropic models has been analysed, following a systematic methodology. To evaluate both advantages and disadvantages of the flow rule, models with similar flexibility (i.e. with 8 and 16 parameters) have been compared by performing a finite element (FE) simulation of a cup-drawing process to study earing phenomena regarding accuracy, computational time and complexity. From the present study, it has been concluded that the main drivers on the final cup-drawing profile prediction are the model flexibility and the coefficient selection rather than the flow rule. Even though the NAFR formulation is complex when compared to the AFR regarding numerical implementation, this study shows that the total simulation time in a cup-drawing process while using explicit FE solvers is reduced in some cases, this one being strongly dependent on the material parameter definition.