Environmental and Mechanical Fatigue of Wind Turbine Blades Made of Composites Materials

Abstract

The problem relevant to fatigue design and analysis of wind turbine blades made of composite materials is faced; mid-size single-blade wind turbine is taken into consideration. Static and fatigue load conditions are defined; hygrothermal conditions are identified as well, in terms of yearly statistical distribution of wind speed and air temperature, relative humidity, solar radiation and atmospheric pressure daily variations, the occurrence of low-energy impacts due to hailstones is also considered. A FEM structural analysis is carried out to compute stress and strain distributions all along the blade: hot spots are identified; the stress critical values, along with fatigue spectra, are used to design fatigue tests. Some preliminary tests are performed on composite specimens previously dry and wet conditioned, as well as on low-energy impacted coupons, considering both mechanical and hygrothermal effects; finally some preliminary fatigue tests on both adhesive and riveted composite joints are carried out.