Mechanism-correlated characterization of the deformation and damage behavior of thermo-plastic-based fiber metal laminates for property-oriented process development

• Applicants: Professor Dr.-Ing. Guntram Wagner; Professor Dr.-Ing. Frank Walther
• Subject Area: Polymeric and Biogenic Materials and Derived Composites ; Materials in Sintering Processes and Generative Manufacturing Processes ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 414332488

The objective of the two-phase research project is the identification, analysis and assessment of influencing factors on the strength and durability of thermoplastic-based fiber metal laminates. The first funding period focuses on material development and the consolidation process. In a second funding period, the effect of forming technology on material integrity as well as component integrity will be investigated by means of a demonstrator component. According to the state of the art, the fatigue strength of thermoset-based fiber metal laminates is influenced, in particular, by their delamination behavior. Therefore, primary objective for the intended qualification of alternative thermoplastic-based fiber metal laminates is the investigation on the restraint of fatigue damage as a result of mechanical (blasting) and chemical (pickling) methods for surface pretreatment of the metallic component. The interfacial and microstructure formation in the fiber-reinforced polymer (FRP) and aluminum layers will be determined by means of materialographic methods, e.g., light microscopy (LiMi), scanning (SEM) and transmission electron microscopy (TEM), as well as computed tomography (CT). The identification of dominant damage mechanisms will be carried out in quasi-static and cyclic testing using extended instrumentation for the monitoring of damage-related physical parameters, e.g. changes in electric resistance and acoustic emission. For a more detailed analysis of damage mechanisms, stiffness gradients in the material volume in quasi-static in-situ tests will be visualized via CT using the novel approach of digital volume correlation (DVC). Based on the results of mechanical testing, a process-structure-property relationship will be formulated and recommendations for the parameterization of the process steps for the production of thermoplastic-based fiber metal laminates will be given. At the end of the first funding period, selected fiber-metal laminates are fundamentally characterized and their damage behavior is investigated systematically. Furthermore, suitable laminate configurations are available as starting material for forming processes which are to be investigated in the second funding period. In the second funding period, the influence of forming processes on the material behavior of fiber-metal laminates is to be determined by means of a formed demonstrator. Specimens will be resected from areas which are influenced, e.g., by fiber rearrangements in bending radius. These specimens will be analyzed under mechanical as well as materialographic aspects. A further focus is the generation of extended stress distri-bution, e.g., by superimposed temperature and humidity influence in fatigue testing, in order to investigate the material behavior under operating conditions.

• DFG Programme: Research Grants