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Study on ductile fracture criterion applied to shear fracture prediction of DP780 sheet

Wu Jiaxiong, Sun Xuguang, Sun Xiaoce, Chang Fu, Yang Shudi, Tan Senqi

Journal of Theoretical and Applied Mechanics

2024

Vol. 62 nr 1

143--156

With the development of automotive lightweight technology, the improvement of the design of body sheet metal forming processes has gradually become a research focus. Advanced high- -strength dual-phase steel is the main material for lightweight vehicle bodies, and exploring its accurate ductile fracture criteria plays an important role in predicting the forming fracture behavior of the sheet metal. The characterizations of the plastic behavior of the DP780 sheet before fracture were performed by the Swift hardening model. Three sets of tests from pure shear to tensile-shear stress states are designed to calibrate the ductile fracture parameters of Lou-Huh, Cockcroft-Latham, and Rice-Tracey criteria. The calibrated parameters are used to predict tensile shear test fractures and punching fractures at small bend fillets of molds. The results show the Lou-Huh criterion can accurately predict the shear fracture behavior of the DP780 sheet in the low-stress triaxiality (0.08-0.33).

Weldability of pulse GMAW joints of 780 MPa dual-phase steel

So W., Kang M., Kim D.

Archives of Materials Science and Engineering

2010

Vol. 41, nr 1

53-60

Purpose: This paper assesses the gap bridgeability of pulse GMAW joints of DP 780 for automobile body. Design/methodology/approach: Wire melting was analyzed using a high-speed camera. The impact of EN ratio on the shape of the bead section was examined after analyzing the macrosection of welding which was obtained on a bead-on-plate-welding experiment. Welding conditions that are robust to the gap were suggested through an analysis on tensile strength, macrosection of the weld and fracture appearance of tensile strength testing at the lap joint welding of DP 780. Findings: A relation among the welding current (welding process parameter of AC pulse GMAW), EN ratio, welding speed and bead shape parameters which include bead width, bead height and penetration were computed. Research limitations/implications: The suitable welding conditions proposed in this paper can change because of types of welding joints thickness of base metal and other reasons. Practical implications: In this study, the suitable welding conditions were presented for securing a good weld quality of DP 780 for the automobile body. Originality/value: Through this study, the correlation between the weld bead geometry and the EN ratio in the AC pulse GMAW was confirmed. Though the weld quality assessment, suitable pulse GMAW conditions of DP 780 were suggested.