On modelling of shear fracture in deep drawing of a high-strength dual-phase sheet steel

Abstract

A new specimen for out-of-plane shear strength of advanced high strength steel sheets B Gu, J He, S H Li et al. Abstract. The paper presents application of fracture behaviour characterisation results of a dual-phase sheet steel DP600 to an FEA of its deep-drawing for shear fracture prediction. The characterisation results were obtained with the help of a characterisation method based on a tensile test on a novel butterfly specimen and published previously by the authors. The aim of the present paper is to evaluate that characterisation method on a deep-drawing process. Based on the previous results of the authors, the fracture behaviour is modelled here with the help of the modified Mohr-Coloumb fracture model. The obtained FEA results reveal that shear fracture of the studied material is predicted too early by the used MMC fracture model. A novel adjustment of the model is proposed yielding infinitely high fracture strains at strongly pressuresuperimposed stress states. As it is often the case in the state-of-the-art fracture characterisation of high-strenght sheet steels, such stress states were not tested during the previously performed fracture characterisation but occur during the studied deep drawing process. With the help of the adjusted MMC fracture model, it is possible to predict the crack initiation moment very accurately and the crack initiation location sufficiently accurately.

Fracture Characterisation by Butterfly-Tests and Damage Modelling of Advanced High Strength Steels

“…In a comprehensive study, Behrens et al compared different experimental methods and discussed the advantages and disadvantages of common tests [7]. In this study and in a further application in [2], a methodology with a special butterfly specimen geometry, which was developed at the IFUM [8], showed good applicability for a DP600 steel. This approach is therefore chosen to be applied in this work for the investigation of the damage behaviour of two other AHSS, a dual-phase DP1000 and a complex-phase CP800 sheet metal material.…”

“…This results in a propensity for different crack appearances, without prior indication by thinning, like exemplary shear fracture on tight radii and edge-fracture, which all can not be predicted by an FLC. These challenges in numerical damage prediction are exemplary demonstrated in [1] and confirmed in [2]. Moreover, the fracture behaviour of AHSS compared to conventional steels, results in a propensity for shear failure as opposed to ductile failure caused by thinning for example during automotive panel stamping.…”

“…The damage accumulation of non-linear loading paths can be considered due to an incremental contribution of the equivalent plastic strain. Model approaches such as Xue-Wierzbicki [4], CrachFEM [5], Modified Mohr-Coulomb (MMC) [6] have shown good results for damage representation of high strength steels, for example for a TRIP690 steel in [1] and a DP600 steel in [2]. In order to parametrise these kind of models, the fracture behaviour has to be identified within different tests under consideration of various stress states.…”

A Review of Sheet Metal Forming Evaluation of Advanced High-Strength Steels (AHSS)

“…Furthermore, the results indicated that the MMC model outperformed the FLC criterion in dealing with NLSPs and shear-induced fracture. Nevertheless, Behrens et al [236] highlighted the significance of considering no damage accumulation effects for stress triaxialities below −0.33 in the MMC formulation. Their study detected premature shear fracture initiation of a DP600 steel workpiece in a deep drawing operation without the aforementioned condition.…”