Influence of Sheet Metal Pre-forming on Edge Crack Sensitivity using an AHSS Steel Grade

Abstract

Especially in the automotive sector, high-strength sheet materials are processed in the manufacturing industry. These steels often show a pronounced sensitivity to edge cracks. Because of this, many edge crack testing methods for a wide variety of stress conditions have been developed to describe the edge crack sensitivity of a material. Only the hole expansion test according to ISO 16630 has been standardized. However, the standardization has some gaps in the process description, which has resulted in test modifications. Another disadvantage is the dependence of the results on the machine operator. In the past, the influence of the shear cutting parameters die clearance, cutting edge geometry, and type of cutting line on the edge crack sensitivity was only calculated for undeformed sheet materials. Not only are shear cutting operations carried out on undeformed sheet blanks in the context of the manufacturing of sheet metal components, but more and more pre-formed sheets are mechanically separated and subsequently further formed. Therefore, it is essential to consider the influence of the type and amount of pre-forming introduced on the sensitivity of a material to edge cracks. The discrete types of pre-forming, uniaxial tension, plane strain, and equi-biaxial stretch forming were introduced to sheet metal blanks using dual-phase steel. The Edge-Fracture-Tensile-Test was used to identify the residual formability of the undeformed and pre-formed specimens. The Edge-Crack-Sensitivity-Factor{K}_{mathrm{ec}}, which can be used to predict edge cracks in a finite element forming simulation, was determined from the recorded major strains for selected parameter configurations.