Investigations on fracture curves in strain and stress space for advanced high strength steel forming

10th International Conference and Workshop on Numerical Simulation of 3D Sheet Metal Forming Processes

Panich, S.^1,2 ; Drotleff, K.^1 ; Liewald, M.^1 ; Uthaisangsuk, V.^3

Institute for Metal Forming Technology, University of Stuttgart, Holzgartenstraße 17, Stuttgart

70174, Germany^1

Department of Production Engineering, Faculty of Engineering, King Mongkut's University of Technology North Bangkok, 1518 Pracharat 1 Road, Bangkok

10800, Thailand^2

Department of Mechanical Engineering, Faculty of Engineering, King Mongkut's University of Technology Thonburi, 126 Pracha Uthit Road, Bangkok

10140, Thailand^3

关键词: Advanced high strength steel;    Anisotropic yield functions;    Deformed samples;    Forming limit curve;    Localized necking;    Optical strain measurement;    Strain and stress;    Stress triaxiality;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/734/3/032066/pdf
DOI  :  10.1088/1742-6596/734/3/032066

来源: IOP

【 摘 要 】

Conventional forming limit curves (FLCs) are inappropriate for describing formability for advanced high strength (AHS) steel sheets, since such steel grades experience fracture without localized necking occurrence. The aim of this work was to develop a fracture curve (FC) for the AHS steel grade DP980. The FC was determined by means of the Nakajima stretch forming test and tensile tests of various sample geometries, by which shear fracture governed. An optical strain measurement system was used to capture strain histories of deformed samples up to failure. From these results, fracture strains were gathered and plotted in a strain space. Subsequently, the strain based curve was transformed to space between stress triaxiality and plastic strain. Hereby, effects of anisotropic yield function, namely, the Hill'48 model on obtained stress fracture loci were investigated. In order to verify applicability of the determined limit curves, a Mini-tunnel part was pressed and simulated. It was found that the stress based FC do predict failure of the DP980 steel sheet more accurately than the strain based F C.