Investigations on edge quality and its effect on tensile property and fracture patterns of QP980

Abstract

Advanced High Strength Steel (AHSS) sheet metals have been widely used in automotive structures due to its safety performance and lightweight potentials, and some AHSS materials have been found more sensitive to edge crack during the stamping process. The tensile property of the sheared edge has great influence on flangability for AHSS. In the present work, the effects of the blanking clearance and shear angle on the quality of the sheared edge and subsequent tensile property for QP980 have been investigated experimentally by microscope and sheared-edge tension test based on digital image correlation (DIC) technology. In addition, the tensile properties of the specimens prepared by wire electrical discharging machining (Wire-EDM) and laser cutting were tested as well. The results show that promising and stable sheared edge quality, and tension with postponed fracture can be achieved if the clearance ratio is set as 7% or 11% for QP980. During blanking with 5° or 10° oblique edge, the ratios of burnish zone and burr zone decrease simultaneously, and the subsequent tensile performance increases significantly. The oblique edge blanking obtains smaller and smoother burr, and the sheared surface benefits from less void damage. In addition, based on the fracture surface morphology and the tracking of the fracture process with DIC technology, two typical fracture patterns (oblique crack and transverse oblique crack) in tension test are illustrated. Oblique crack occurring on the specimens with good edge quality shows obvious necking phenomenon and belongs to the typical ductile fracture. While transverse oblique crack exhibiting with high frequency on the sheared specimens is typical edge fracture and shows mixed characteristics of ductile fracture and brittle fracture.