FORMING LIMIT OF STAINLESS STEEL-CLAD ALUMINUM SHEETS UNDER PLANE-STRESS CONDITION

The forming limit of sheet metal laminates under biaxial stress condit ion is investigated A criterion of localized necking for the laminates , in the negative strain-ratio condition (beta = epsilon(2)/epsilon(1) less than or equal to 0, epsilon(1): major strain and epsilon(2): min or strain), is derived based on Hill's theory of localized necking. Fo r biaxial stretching (beta = epsilon(2)/epsilon(1) > 0), a modified Ma rciniak-Kuczynski-type analysis, which assumes that an initial inhomog eneity in a sheet appears at the onset of the diffuse necking, and it develops into localized necking, is conducted with the consideration o f void growth in the groove of the sheet. The calculated forming Limit diagrams (FLD) are compared with the corresponding experimental resul ts determined by punch-stretching experiments on two- and three-ply st ainless steel-clad aluminium sheets. Both in the analytical prediction s and the experimental observations, the FLDs of the laminates lie bet ween those of their component sheet metals. The effect of prestrain ge nerated in the roll-bonding process on the formability is discussed.