A Study of the Plastic Deformation of Sheared Edges of Dual Phase 780 Steel
One of the concerns for advanced high strength steels (AHSS) in stamping operations is the failure of sheared edges in stretching modes. When a forming operation requires stretching edges, local formability becomes a very important factor of the material application, particularly for the AHSS. The local formability of a material is usually characterized by the hole expansion ratio (HER). During edge stretching, the sheared edge can be in contact with the tool or it can be free. These two conditions can be simulated by the hole expansion (HE) test using a conical punch and a flat bottom punch, respectively. In this study, the local formability of a dual phase (DP) 780 steel is evaluated using the HE test. The hole expansion tests were performed using a digital record and measurement system (DRMS) which allows the measurement of the final diameter of the hole at the moment of a localized fracture or a through-thickness crack at the hole edge.