Abstract
This tutorial paper presents a load spectrum and an engineering analysis from first principles for estimating the fatigue life of GRP blades of horizontal axis wind turbines. The distributions of aerodynamic loads, which affect the fatigue life of the blade, are analyzed using strip theory. The stiffening effect on a rotating blade is discussed using the multi-body dynamics method. The influences of this dynamic stiffening effect and composite material anisotropy on the blade vibration modes are analyzed. Then, the dynamic stress response caused by the deterministic dynamic loads, such as aerodynamic load, gravitational load and rotating centrifugal load etc, is calculated using finite element modal superposition method. Fatigue damage performance, fatigue damage rule and the fatigue life estimate method for GRP blades are included. Finally, applying the Palmgren Miner rule for linear fatigue damage accumulation, an estimate of safe working life is made. The fatigue life estimate for a 1.5 MW wind turbine GRP blade agrees with physical experience. The paper is presented as a didactic example for the methods used.