Issue 75

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

Of greater interest is what happens subsequently, when a clear difference between the two lubrication methods is noted: without lubricant, the thickness in zone D does not decrease further, while a significant thinning occurs between the punch and the blank holder (zone C) that continues until failure. For the specimens lubricated with PVC film, the reduction in thickness underneath the punch (zone D) continues until the sheet metal cracks. Lubrication also allows for better strain distribution, resulting in a significant reduction in thickness in areas B and C, as well as D. The FEM simulation also highlighted that, unlike AISI 430, AISI 304 shows a significant thinning near the knee (area B) and a slight reduction in thickness in the area beneath the blank holder (area A). These differences are due to the higher plastic deformability and high work hardening coefficient of AISI 304, which allow it to distribute both stresses and strains more effectively and homogeneously than AISI 430.

Figure 17: Von Mises stresses predicted by the FEM analysis immediately before the spherical cap failed. To allow comparison between the different experimental conditions, the measurement position was normalized with respect to the length of the deformed zone between one of the two blank holders and the apex of the spherical cap. Position 1 indicates the apex of the cap, while position 0 indicates the blank holder. The image only considers the half of the cap not affected by failure.

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