Forming behaviour of sheet steel laminate

Steel sheets bonded with a thin layer of a polymeric adhesive are used for their sound-deadening effect in applications such as machine enclosures and automobile bulk-heads. Unlike sandwich materials designed primarily for high rigidity, they are formed by conventional methods and the effect of the relative inability of the adhesive to transmit shear on formability of the sheet and conformity to the tool profile is important. The adhesive in sheet steel/adhesive/steel laminate used for acoustic damping displays viscoelasticity only at small strain, and strain hardening is associated with subsequent viscous flow. High forming speed is favourable to the forming of steel sheet laminate bonded with a viscoplastic polymeric adhesive because it increases the ability of the adhesive to transmit shear forces, which in turn increases the transverse stiffness of sheet laminates, although it increases springback (decreases the shape fixability of the laminate). At elevated temperature, the softening of the steel sheets as well as that of the adhesive is significant, decreasing the rigidity but improving the shape fixability of the laminate.