Fatigue of polymer composites under cyclic thermal loads

• Applicants: Dr. Gerhard Kalinka; Professor Dr.-Ing. Michael Sinapius
• Subject Area: Mechanics ; Lightweight Construction, Textile Technology
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 379482657

The scope of this project is the fatigue behaviour of CFRP subjected to cyclic thermal loading conditions. It is expected that fatigue under cyclic thermal loads occurs due to the thermally induced inter- and intra-laminae internal stresses. These residual stresses are induced both by the different coefficients of thermal expansion of the fibre and the matrix material on the micro scale as well as by the different thermal expansion behaviour of adjacent plies with different fibre orientation in a multi-layered laminate on the macro scale. The working hypothesis of this research project is that the thermal loads can be represented by an equivalent mechanical stress state. Using this equivalent stresses, the thermal load can be treated within a fatigue damage model similarly to mechanical stresses. With the approach proposed in this project, the thermally induced stresses on the micro scale are being considered in a ply-based macroscopic fatigue damage model. Within current fatigue damage models, these stresses are typically neglected as they are not captured with the classical modelling techniques. Based on this hypothesis, the fatigue damage mechanisms under cyclic thermal loading conditions are investigated. Therefore, experimental tests are conducted to systematically analyse the damage mechanisms starting at the scale of a single fibre up to the macro scale examining a multi-layered laminate. The transfer of the experimental findings into mathematical models and simulations offers the opportunity to thoroughly understand the underlying mechanisms and to explain the observed phenomena. From the knowledge gained from these experiments and simulations, an approach is derived which transfers the thermally induced micro scale stresses to the macro scale, thus enabling the consideration of the micro stresses in a macroscopic fatigue model.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Tobias Wille