Strain Evolution during Stretch Forming with a Hemispherical Punch in 5052 Aluminum Alloy Sheets

During plastic deformation, 5000 series aluminum alloys often exhibit serration and the Portevin-Le Chatelier ( PLC) bands. The occurrence of the PLC bands is affected ff ected by strain paths, but the details are not understood. In this study, the effects ff ects of strain ratios on the PLC bands during hemispherical-punch stretch forming were investigated in 5052 aluminum alloy sheets. Strain evolution was measured using a digital image correlation method. When the strain ratio was close to uniaxial tension, the strain evolution was not uniform and apparent PLC bands were observed. By contrast, PLC bands were less pronounced under pseudo-plane-strain tension and were not visible under pseudo equibiaxial tension, showing that PLC bands became more difficult ffi cult to appear as the strain ratio approached equibiaxial tension. The difference ff erence in the appearance of PLC bands occurred presumably because of the difference ff erence in the strain rate depending on the strain ratio. However, PLC bands were observed clearly at a strain rate similar to that under equibiaxial tension, suggesting that the strain rate at which PLC bands appear could differ ff er depending on the strain ratio.