Sandwich panel has been widely applied to enhance the stiffness to weight performance of components in many industries. The manufacturing procedure of curved metal sandwich panels typically consists of forming the sheet and core material into prescribed shapes and applying the adhesive to bond the material in shaped molds. An alternative manufacturing method is to apply the conventional sheet metal forming technique to deform the flat sandwich panel into a curved panel. However, the face sheet will significantly limit the formability of the sandwich panel. To solve the problem, one face sheet was removed in the sandwich panel to increase the formability, then the metal sheet and the metallic open-cell foam were selected as the face sheet and the core material to form the metallic open-cell foam supported sheet metals.
The main objective of this study is to develop a proper forming method to deform the metallic open-cell foam supported sheet metal without failure occurring. Two forming processes, press brake bending and hydroforming, which can reduce the contact stress to avoid the structure damage were investigated. Experiments were designed to understand the possible failure modes and the failure mechanism. Through the parametric study in the experimental results, the effects of material dimensions, material properties, and test parameters were analyzed to establish a failure criterion. In addition, a finite element analysis with a proper foam model was implemented to further inspect the failure mechanism and develop a guideline for the selection of materials and test parameters.
For the press brake bending process, the experiment results have shown that the supported sheet metal can be successfully bent into a curved panel within small thickness reduction. The prediction in both geometric hoop strain failure criterion and shear strain failure in the finite element analysis were matched and agreed with the experimental result. For the hydroforming process, the experimental result indicated that the major failure mode is the adhesive failure. The early adhesive failure at the perimeter of the attached foam disc caused the open-cell foam to separate from the sheet metal. The required adhesive strength to the attainable dome height relationship was given by finite element analysis
