A critical review on hole expansion ratio

Materials resistance to edge fracture in intricate shape forming is commonly quantified by hole expansion ratio (HER). Hole expansion test is normally used to evaluate HER. To date, the governing factors of HER have not well understood regardless of its importance for automotive part manufacturing with advanced high-strength steels. The present paper comprehensively discussed the recent progress on HER, including fundamental deformation aspects, the effect of punch geometries, correlation with tensile properties, and the influence of microstructure. This reviewed work explains why HER is currently an essential topic of engineering research.