Formability of Sheet Metal Laminates Consisting of Layrs of Less Formbility or Weak Laminate Boundaries

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This research project deals with the formability of sheet metal laminates consisting of layrs of less ductility or weak laminate boundaries. The results are summarized as follows.(1) The forming limits under biaxial stress conditionas are determined based on Hill's theory of lacallized necking and the M-K theory. The minimization of reduction of sheet thickness in roll bonding operation is required since the roll-bonding induced prestrain makes the formability considerably less.(2) The fracture load in stretch bending becomes lower with decreasing die-radius. For a two-ply laminate, the fracture load is higher for a weak-layr (outside) /strong-layr (inside) laminate compared with the laminate of reversed configuration.(3) If chromium (whose DBTT is over 150ﾟC) is clad by some appropriate metals, the clad can be plastically bent at comparatively lower temperature. For example, chromium (outside) /aluminium (inside) laminate can be bent at 50ﾟC,because the stress in the chromium layar is reduced due to the movement of the neutral surface.(4) A new testing method of bending of a laminate with a slit is proposed for evaluating the bonding strength of sheet metal laminates.