Issue 75

A. Casaroli et alii, Fracture and Structural Integrity, 75 (2026) 179-199; DOI: 10.3221/IGF-ESIS.75.13

of a solid lubricant with a PVC film dramatically changes the strain profile, which, in both directions, is similar and increases almost steadily up to the tip of the punch. In this case, deformation occurs everywhere due to balanced biaxial stretching. In specimens lubricated with PVC film, both longitudinal and transverse strains take on a "single bell" shape, with maximum deformation and failure occurring near the apex of the spherical cap. The type of stainless steel also plays a significant role: AISI 304, thanks to its greater plastic deformability and high work hardening coefficient distributes deformations better than AISI 430. Similar considerations can also be extended to the thickness of the sheet metal, summarised in Fig. 13 on the side of the spherical cap not affected by the fracture.

Figure 12: Planar deformations of the spherical cap generated by the Erichsen test. To allow comparison between different experimental conditions, the measurement positions were normalized with respect to the total length of the deformed zone. Position 1 indicates the apex of the cap, while positions 0 and 2 correspond to the blank holder. The circles shown below the graphs indicate the deformation of the sheet metal at each measurement point.

191