Issue 75

A. Casaroli et alii, Fracture and Structural Integrity, 75 (2026) 104-123; DOI: 10.3221/IGF-ESIS.75.09

Hardness tests The metallographic samples were also used to evaluate the HV0.2 (0.2 kg f , 15 s) Vickers microhardness according to standard ISO 6507. The tests were performed on ten different areas, shown in Figure 12, in order to characterize the hardness on the Erichsen samples for both the stainless steel types (AISI 304 and AISI 430) and the lubrication methods (without lubrication and with PVC film). For each area, the hardness was evaluated near the inner and outer edge of the sheet metal and at half of its effective thickness. Specifically, areas 1 and 2 refer to the stainless steel under the blank-holder, areas 3 and 4 are located near the knee just beyond the blank-holder, while areas 5, 6 and 7 are located in the contact-free area between the blank-holder and the punch. Areas 8, 9 and 10 are instead representative of the spherical cup produced by the punch.

Figure 12: HV0.2 microhardness profiles along the Erichsen samples (areas 1 to 10) already used for metallographic analyses. The DRY conditions were obtained without lubrication, while the LUBRICATED conditions were obtained by applying the PVC film in the punch and blank holder areas. In both cases, the punch speed and the blank holder pressure were set equal to 4.3 mm/min and 6.6 MPa respectively.

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