Characterization of laser-cut carbon fiber-reinforced polymers with regard to tension-compression and bending fatigue loading for simulation-based fatigue life prediction

• Applicants: Dr.-Ing. Peter Jäschke; Professor Dr.-Ing. Frank Walther
• Subject Area: Polymeric and Biogenic Materials and Derived Composites
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 436398518

The second funding period aims at the characterization of the influence of thermal damage during laser beam cutting (LBC) of carbon fiber-reinforced polymer (CFRP) on the fatigue behavior under axial and bending loading and to simulate the damage evolution with regard to a fatigue life prediction (taking into account all data, including the first funding period). The modeling of CFRP fatigue properties, while taking into account superimposed LBC-induced damage due to high local energy input, is a key aspect. The different types of damage caused by axial and bending loading make it difficult to simulate the LBC-induced reduction in fatigue life and must be known for predictions. A basis for evaluating the suitability of LBC for sustainable CFRP component cutting will not be available until the project has been completed. Therefore, the following central research hypotheses need to be evaluated: 1) The evaluation of the mechanical characteristics combined with microstructural characterization of the damage states enables the identification and cause assignment of the stress-dependent damage evolution in LBC-CFRP for the qualitative and quantitative description of the fatigue behavior (WPT). 2) The properties of the laminate components can be mapped with sufficient accuracy for the fatigue life predictions of multidirectional laminates using damage levels based on the damage mechanisms occurring after the LBC and the mechanical load (LZH). The following research question can be derived from these central research hypotheses: Can the influence of LBC on the mechanical fatigue properties of multidirectional CFRP be sufficiently simulated and modeled to ensure a valid assessment of resulting material properties for fatigue life prediction? For this purpose, after the production of defined test specimens, the LBC states set in the CFRP are to be identified by microstructural investigations and their influence determined in quasi-static tests on uni- and multi-directional laminates for the initial modeling of the FEM simulations and their validation. In addition, load type, intensity and time-dependent fatigue properties of the LBC-CFRP are determined mechanism-based using metrological instrumentation and microstructural analyses. As a result, LBC-related failure mechanisms, the damage evolution and associated limit values for fatigue loading capacity will be available. Waterjet-cut specimens serve as a reference to LBC in order to ensure that the LBC damage mechanisms can be differentiated. The data generated on fatigue behavior is incorporated into the incremental fatigue life prediction and is used for final validation.

• DFG Programme: Research Grants