Analysis of forming limit diagram for superplastic materials

Superplastic materials show very large tensile elongation (in excess of 5000%) even if they are lowly stressed. Superplastic forming is carried out at high temperatures and relatively low strain rates. In order to control the industrial forming processes, the difficulty in predicting the failure strain of superplastic materials is main problem faced by technologists. In this paper, limit strain for superplastic materials were investigated under biaxial tension using the finite element method (FEM). To validate the results biaxial tension tests have been conducted using a fine-grained Pb-Sn alloy that shows superplastic properties at room temperature. The superplastic sheet was deformed using an experimental apparatus with dies of aspect ratios of 1:1, 15:11, 5:3 and 5:2.