Design of bendable sandwich sheets with 3D printed CFRP cores via multi-stage topology optimization

Abstract

The applications of sandwich structures are mainly limited to flat panel types due to their poor bendability. To develop bendable sandwich sheets, a new design strategy was proposed in this study, in which the density-based topology optimization was integrated with the multi-stage genetic algorithm (GA) to optimize the material layout so that the sandwich topologies can withstand potential failures including core shear failure, core-face sheet delamination and face buckling at given bending conditions. The topology optimization problem was mathematically formulated based on theoretically deduced failure constraints on core shear failure, face buckling and core-face sheet delamination. The adaptive multi-stage GA was adopted to solve the topology optimization problem with massive design variables and generate optimized topologies with sufficient resolutions to be additively manufacturable. The optimal topologies at given volume fraction constraints were additively manufactured using carbon fibre reinforced nylon (Onyx) and bending tests were conducted to check the bendability. Results indicate that topologically optimized SUS304/Onyx/SUS304 sandwich sheets can be bent without failure, which demonstrates the validity of the proposed topology optimization strategy. The proposed method is potentially capable of designing bendable sandwich sheets with arbitrary material combinations and is expected to expand the application envelope of lightweight sandwich structures.