Frequency effect in multiaxial fatigue behaviour of a structural steel for offshore wind turbine support systems
Abstract
Fatigue analysis is fundamental to ensure structural integrity of support systems of offshore wind turbines, since wind, waves, working loads, among others, are usually cyclic and lead to cumulative damage. However, design standards of offshore structures do not take into account multiaxial stress states in fatigue analysis. Moreover, very high cycle fatigue regime (VHCF) has been gaining interest due to sustainability goals to extend service lives of structures. Ultrasonic fatigue testing systems are commonly used to assess this regime, since they can achieve a frequency of testing usually around 20 kHz. Nonetheless, this technology brings challenges such as specimen’s design, overheating and frequency effect. The last topic mentioned is particularly relevant since it can compromise the validity of experimental data estimated at higher frequencies. The frequency effect in multiaxial fatigue data is not well described in literature. Therefore, in this work, frequency effect in multiaxial fatigue behaviour of S690 steel is analysed to include it in experimental fatigue data. Experimental tests were performed at different frequencies of testing and under multiaxial loading conditions.
