STUDY ON FORMABILITY OF SHEET STEEL.

The formability of two sheet steels, SSPDX (0. 8 mm thickness) and SPMY (0. 9 mm thickness), are examined by means of a plane-strain tensile test and an in-plane stretching test. The parameters m on Hill's non-polynomial yield function is calculated by applying Wagoner's method. The assumption m equals 2 is recognized for both steels because the difference between effective stress-strain curves of the uniaxial and plane-strain test can almost be neglected. The experimental data of the in-plane stretching test are good agreement with those predicted by modified M-K analysis. Because of less surface roughness growth, the limit strain for SSPDX is greater than that for SPMY. The fracture mechanism of the in-plane stretching specimen observed is almost identical to those for isotropic fcc metals reported.