Failure Orientation in Stretch Forming and Its Correlation with a Polycrystal Plasticity-Based Material Model for a Collection of Highly Formable Sheet Steels

Abstract

Robust design optimization techniques have been developed in recent years within the automotive industry with the aim of reducing scrap rates and improving process stability in sheet metal forming. These new techniques are able to take process variations and other sources of material scatter into account. Among the many material variables and inputs used, the yield criterion is an important aspect and this is used to describe the plastic behavior of sheet metals. To achieve a reliable output in an optimization study, the yield criterion selected must be representative of material response and scatter. However, simple material models that deviate from real material behavior are often used due to a lack of material data, which is usually a requirement when using more complex models. In the present research, a polycrystal plasticity-based CTFP model has been evaluated in stretch forming for a collection of highly formable sheet steel materials. The results demonstrate that the CTFP model can capture the yielding character and also detect the minor deviations presented by different coils. The stretching factor derived from the CTFP model, as opposed to the work hardening and ductility, has a dominant effect on failure for a collection of materials with similar mechanical properties.Results also indicate that plastic deformation causes texture evolution and, consequently, an evolving yield locus. Such changes in the yield locus during deformation have an effect on stretching and friction calibration in FE simulations.

Optimization of Crystallographic Texture for Sheet-forming Applications Using Taylor-based Models

“…Another example is the work of An et al, where different versions of the Taylor model were used for the calculation of yield loci used in FE simulations. [23] Nevertheless, the Taylor theory also has some limitations. For example, Wu et al showed that the method does not produce acceptable results when applied to prestrained aluminum.…”