Wind turbine rotor blades are manufactured using fiber reinforced polymers (FRP). The modern lightweight material excels in terms of its high strength compared to low weight and can be used to produce complex shell structures with a good surface quality. FRP are therefore optimal for aerospace as well as wind turbine rotor blade applications, where the aerodynamic design is especially important.
Isotropic, metallic materials under mechanical load are insensitive to temperature changes in the range of -40°C o +70°C, which corresponds to the field of application of wind turbines. Contrastingly, the thermal expansion behavior within FRP varies between the 10 µm thick glass fibers and the surrounding epoxy resin. Thus, even a temperature change alone, but especially in combination with mechanical load, can lead to damage of the material in the formation of microcracks, which in turn decrease the service life of rotor blades. As a result, complex material tests have to be carried out at different ambient temperatures in order to be able to approve an FRP for the expected service life.
Within the framework of a DFG-supported research project pursued by the division 5.3 for Polymer Matrix Composites, Department 5 for Materials Engineering, an analytical material model was successfully created which allows for the prediction of crack formation and fatigue behavior of FRP based on the measured thermal expansion properties of the reinforcing fibers and matrix. The team around Prof. Dr. Volker Trappe and Dr. David Kraus can show that it is sufficient to carry out complex strength and fatigue tests merely at room temperature, and to calculate the temperature influence that affects the service life, allowing for a significant reduction of the experimental verification needed for a new FRP, as well as saving time and money.
Transverse damage in glass fiber reinforced polymer under thermo-mechanical loading
David Kraus, Volker Trappe
published in Composites Part C, Volume 5, S.100147, July 2021
BAM division Polymer Matrix Composites