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ComMUnion at American Society for Composites (ASC) 33rd Annual Technical Conference

ESI GROUP at ASC presenting results of ComMUnion project in the conference Multi-scale analysis of joints in hybrid metal/composite structures in ESI VPS

The lack of maturity of crash simulation of structures made of hybrid materials is a key issue for lightweight engineering in automotive industry. Tailoring local behavior by mixing materials and accounting for this mix and joining problematics in the simulation methodology are required to optimize weight and costs, without the need of a real prototype. As of today, lightweight vehicle programs call for local strengthening of structural body components through hot or warm formed high strength steels with spot-welded joints. New metals or composites parts with new adapted joining techniques are progressively introduced for the next stage of weight saving. Local reinforcement by thermo-plastic composites is also considered to offset costs trade-offs. The present contribution proposes to numerically investigate joints in a hybrid structure using detailed models, then implemented at the industrial component level in a multi-scale approach.
Local strengthening of steel parts through hot forming leads to poor metallic joints with a high crack risk due to local metallurgy changes during welding. In a first step, a welding process simulation is performed to predict the local heat degradation of the material and corresponding mechanical behavior in the joint. Failure prediction on the detailed model allows two options: macroscale models adapted to efficient car crash models with 1D simplified beam connector, or a multiscale approach with a detailed 3D model for more accurate zooming on specific areas. Reinforcement of steel components is investigated in the specific case of laying thermoplastic composite tapes (using the ATL –Automatic Tape Laying - process). An important parameter for the structural strength is the texture of the metal surface. It is linked to both the texturing process and the laying of the thermo-plastic tapes. A microscale model of the textured metal and composite interface is built automatically based on real-life micrographs. It is then used to assess microscopic damage evolution near the interface and to numerically characterize the joint and build up macro scale cohesive zone elements. A mixed material structural component is then evaluated with metallic and composite to metal virtually-characterized joints.