Cavitation during multiaxial deformation of superplastic forming

Uniaxial tension specimens were pulled to a prescribed strain at a constant baseline strain rate. These specimens were sectioned after testing to determine the extent of internal cavitation using digital image analysis. A void fraction evolution equation accounting for the nucleation and growth of voids during uniaxial deformation was derived. The experimental void fraction data was in good agreement with the proposed model. Cavitation in this alloy was found to be a function of strain rate, and more voids were seen at high strain rates. Pressure-time histories predicted using the finite element method were applied to a modified 5083 aluminum alloy in a superplastic press, and partial and fully formed trays were produced. These trays were sectioned and polished, and micrographs were taken to show the cavities in various sections of the tray. Experimental investigations focused on studying the effect of plane strain and general multiaxial deformations on the evolution of cavitation. The plane strain state of stress that occurs in the middle of the tray was more damaging in terms of the evolution of cavitation that the general multi-axial state. Through-thickness variation of cavity void fraction was observed in the entrance radius and the bottom radius regions of the formed tray. It was also observed that the application of hydrostatic pressure was beneficial in reducing cavitation levels.