Necking condition of layers in clad sheets during rolling

In rolling of clad sheets, layers often show periodical necking in the rolling direction. Mechanism of the plastic instability has not been understood sufficiently so that commercially available combinations of layers are limited. First, effects of rolling conditions on the necking were investigated through finite element analysis of some ideal rolling cases. Meanwhile, multi-pass cold rolling of three type of sandwich sheets was conducted to reveal necking evolutions experimentally. Based on the FE and the experimental results, a plane-strain compression model was proposed to simulate the experiments. The predictions based on change in strain energies show good agreement with the experiment.