The mechanical behavior of adhesively bonded tailor-made blanks

Joining (or welding) and subsequent forming of sheets with different thicknesses and/or materials into single-sheet assemblies called tailor-made blank (TMB) is a promising weight-saving strategy for both the automotive and aircraft industries. Although this technology is widely accepted in the automotive industry, it has yet to be applied in the aircraft industry. This is partly because the high-strength aluminum alloys used in the aircraft industry are sensitive to the high welding temperatures. Adhesive bonding is a promising alternative joining method for fabrication of tailor-made blanks in the aircraft industry. In this paper, the mechanical behavior of adhesively bonded tailor-made blanks is studied from both experimental and numerical viewpoints. Transition line is defined as the boundary between two different thicknesses present in the TMB. Two different forming directions, one in parallel with the transition line and one perpendicular to that, are considered. Tensile testing of the specimens from each category is carried out and finite element method (FEM) models are used to simulate the mechanical behavior of the specimens during the test. It is shown that when loading direction is perpendicular to the transition line, metal failure is preceded by decohesion. The adhesive layer is modeled by using the cohesive interface elements with the capability of simulating the damage initiation and evolution mechanisms of adhesives. The experimental and numerical results are compared and are shown to be in a good agreement. It is shown that the capacity of TMBs for in-plane plastic straining is limited. It is therefore recommended that the forming process should be designed such that in-plane plastic straining is minimized.