Abstract The forming limit of sheet metal laminates under biaxial stress conditions is investigated. A criterion of localized necking for the laminates, in the negative strain-ratio condition ( β = e 2 / e 1 ≦0, e 1 : major strain and e 2 : minor strain), is derived based on Hill's theory of localized necking. For biaxial stretching ( β = e 2 e 1 >0), a modified Marciniak-Kuczynski-type analysis, which assumes that an initial inhomogeneity growth in the groove of the sheet. The calculated forming limit diagrams (FLD) are compared with the corresponding experimental results determined by punch-stretching experiments on two- and three-ply stainless steel-clad aluminium sheets. Both in the analytical predictions and the experimental observations, the FLDs of the laminates lie between those of their component sheet metals. The effect of prestrain generated in the roll-bonding process on the formability is discussed.
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