Experimental Investigation and Finite Element Modeling of Hybrid-Formed Steel/Long-Fiber-Thermoplastic Hybrid Components

Abstract Hybrid structures made of metal sheets and FRP offer high lightweight potential and can contribute to lower CO 2 emissions resulting from automotive structural parts. To realize intrinsic hybrids, a hybrid forming method was introduced that combines LFT compression molding and sheet metal stamping, as well as adhesive bonding, in one manufacturing process step. Stiffness-based design and simulation approaches for hybrid parts are already state-of-the-art. However, plasticity and failure are rarely considered which is the topic of this work. For this material modeling, first, a long fiber-reinforced PA6 GF40 material (LFT) suitable for hybrid forming was mechanically characterized, and the joining properties between steel and LFT, realized by a bonding agent, were determined. The hybrid-formed steel–LFT U-profile showed up to 92% higher specific energy absorption in comparison to mono-material profiles under bending. In addition, pure PA6 GF40 designs showed brittle behavior and rapid failure propagation under bending load, whereas steel–LFT hybrid structures showed fail-safe behavior. The corresponding FE modeling for hybrid forming, which does not need complex integrative simulation but offers sufficient accuracy to predict failure of hybrid formed structures was developed. This strategy involves LFT with failure by considering the stress state dependent Johnson-Cook failure criterion, and use LAW83 along with the corresponding SN-Connect failure model for the bonding zones between steel and LFT. The study found that the failure and force-displacement/torque-torsion angle curves in a hybrid-formed U-profile can be predicted with acceptable accuracy.