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Based on findings from micromechanical studies, a Ductile Failure Criterion (DFC) was proposed. The proposed DFC treats localized necking as failure and critical damage as a function of strain path and initial sheet thickness. Under linear strain path assumption, a method to predict Forming Limit Curve (FLC) is derived from this DFC. With the help of predetermined effect functions, the method only needs a calibration at uniaxial tension. The approach was validated by predicting FLCs for sixteen different aluminum and steel sheet metal materials. Comparison shows that the prediction matches quite well with experimental observations in most cases.

A ductile failure criterion (DFC), which defines the stretching failure at localized necking (LN) and treats the critical damage as a function of strain path and initial sheet thickness, was proposed in a previous study. In this study, the DFC is revisited to extend the model to the low stress triaxiality domain and demonstrates on modeling forming limit curve (FLC) of TRIP 690. Then, the model is used to predict stretching failure in a finite element method (FEM) simulation on a TRIP 690 steel rectangular cup draw process at room temperature. Comparison shows that the results from this criterion match quite well with experimental observations.

Hot stamping or so-called continuous press hardening is a process to make sheet metal parts with yield-tensile strength up to 1150Mpa-1550Mpa. Due to the high specific ratio of quenched Boron steels, which is higher than those of aluminum alloys and magnesium alloys, the components with low mass can be made from hot stamped Boron steels. In current industrial practice, direct hot stamping process, which forms a part directly from a flat sheet blank, is normally used to make geometries with relatively mild deformation, such as B-pillars, A-pillars etc. In this study, indirect hot stamping is introduced to develop geometries with a deep cavity and complex form features. Since the indirect hot stamping develops the part cavity depth in cold drawing and then forms detail features in hot stamping, part with complex geometry can thus be formed. A rocker component is chosen to demonstrate the technology.

Sheet metal forming at elevated temperatures, or so-called sheet metal warm/hot forming, is a relatively new forming process to make sheet metal parts with low mass. An accurate and convenient description of forming limit is critical for the success of forming process design and improvement. Strain-based Forming Limit Diagram has long been used to describe forming limit in cold sheet metal forming. However, at elevated temperatures, the formability of those sheet metals is strongly governed by both temperatures and strain rates. In order to extend the Forming Limit Diagram method into elevated temperature domain, a large number of forming limit curves are intuitively required to cover different temperatures and strain rates. It is not only costly to obtain but also inconvenient to apply those forming limit curves in industrial practice.