0052-02-Crystal plasticity and phenomenological approaches

Crystal plasticity and phenomenological approaches for the simulation of deformation behavior in thin copper alloy sheets

The current trend for product and device miniaturization has promoted micro-scale manufacturing processes. The demand for microparts has significantly increased in the automotive and electronics industries. Due to their suitability for mass production, sheet metal forming processes are widely used in the manufacturing industry and have been applied to very thin sheets. However, microforming raises a number of challenges related to the size of the parts targeted and the submillimetric thickness ofthe sheet metals (Geiger et al., 2001). Finite element based simulations are nowadays common engineering tools. They allow to assess manufacturability of parts and to achieve subsequent time savings at the process design stage. Yet, the quality and predictiveness of these simulations rely on several factors, among which is the material behavior model. Currently, two distinct material modeling approaches can be considered for sheet metal forming

On one hand, the so-called phenomenological models are based on discrete macroscopic experimental observations and the assumption of material homogeneity. The constitutive laws consist of sets of relations with parameters which are adjusted to reproduce the experimental data available. Commercial finite element packages include several phenomenological laws for material modeling. Following the still extensively used von Mises model, quite a number of functions have been proposed to take into account anisotropy in the prediction of plastic yield.

On the other hand, the so-called microstructural models are based on the crystal plasticity theory.

Presently, although they provide a physically based simulation framework, microstructural models are not available in commercial software. The phenomenological approach truly represents the standard constitutive modeling choice for in- dustrial process simulations. Indeed, in addition to their computational efficiency, the latter approach has proven reliable and predicitive enough for most industrial applications.

Nevertheless, when it comes to processes involving very thin sheet metals with a few grains in the thickness, usually termed as ultra-thin sheet metals, phenomenological models often fail to render material behavior