Modeling the anisotropy evolution in sheet metals with heterogeneous properties

The adoption of local heat treatments to effectively modify the material behavior is an interesting solution for improving the formability limits of sheet metals during complex forming processes. Being the Finite Element approach the most effective way to design the material modification, in this study we develop a comprehensive constitutive framework to describe the spectrum of plastic responses associated with different levels of annealing, while considering the effect of the anisotropy. Both changes of the flow stress and the anisotropy with the level of annealing are modeled using sigmoidal functions and introduced in a metal plasticity anisotropic model (Hill48). This approach provides a constitutive framework that, relying on a limited number of experimental characterization tests, allows to predict the evolution of the yield locus according to the level of annealing experienced by the material during the heat treatment. The proposed approach revealed to be an effective tool for modeling the spectrum of heterogeneous mechanical responses, particularly valuable, for instance, in the context of local heat treatments, such as laser -based methods or welding processes. It allows to capture the material behavior in terms of R -values distribution, not only in the region irradiated by the laser spot but also in the transitional region. The detailed hybrid numerical/experimental methodology allows to plug-in any anisotropic plasticity model, making the constitutive framework extremely versatile and needing a very limited number of tests. The calibration of the model from experiments and the accuracy of the predictions are thoroughly discussed.