Fracture characteristics of advanced high strength steels during hole expansion test

This study was performed to estimate the stretch-flangeability of two important advanced high strength steel (AHSS) sheets, i.e. DP980 and TRIP1180, using hole-expansion test (HET). Moreover, the effect of hole edge-quality on stretch-flangeability of both steels was analyzed by adopting two different methods, (i) shearing and (ii) wire cutting, to create the central hole on test specimens. Formability of the sheets was measured in terms of fracture strain and hole expansion ratio, under the influence of two different edge-qualities. A detailed characterization at both micro- and macro-scale was carried out to analyze the fracture behavior of both steels. Experimental results showed that the role of localization and shear in addition to edge-quality is crucial to fracture behavior of both the steels. Apart from the macro- and micro-scale characterization, a finite element study was also carried out to model the HET numerically. Finally, a suitable fracture criterion was used to predict the onset of fracture during the test.