Analysis of the Hole Expansion Characteristics of a DP800: Experimental Results on Dwell Time Dependence after Shear Cutting

The present study investigates the hole expansion behavior of an advanced high-strength steel (AHSS) following the ISO 16630 standard. The hole expansion test is an established method for evaluating the formability of shear cut edges of sheet metal material. This study is specifically focused on examining the impact of dwell time between shear cutting and the hole expansion test on the hole expansion ratio. The material investigated in this study is the AHSS grade CR440Y780T-DP GI50/50-U (DP800). The DP800 material is renowned for its exceptional strength and formability and is, therefore, widely utilized in automotive structural components. As a consequence, it has become a critical subject for analysis and has been established as a benchmark material for the hole expansion test. In the experiments conducted in this study, holes were created using a shear cutting tool. After the shear cutting process, controlled tests were performed to evaluate hole expansion at varying dwell times between those steps, ranging from ten minutes up to four weeks. The tests were conducted under standardized conditions to ensure reproducibility, and the hole expansion was measured using digital image correlation and compared with wire-cut holes. The findings demonstrate that the dwell time duration between the two processing stages notably impacts the hole expansion ratio of the DP800, with extended dwell times resulting in reduced expansion ratios.