Accelerated full scale fatigue testing of a small composite wind turbine blade using a mechanically operated test rig

A 2.5m long glass fibre reinforced plastic composite wind turbine blade was fatigue tested by means of a mechanically operated test rig. The rig uses a crank eccentric mechanism to flex the blade by a constant displacement in the flapwise direction for each load cycle. A yearly fatigue-loading spectrum for the blades has been developed from using short-term detailed aeroelastic and wind measurements, results from a detailed finite element model of the blade and averaged long-term wind data form the Australian Bureau of Meteorology. This spectrum contained over 200 load levels covering R ratios from 0 to 0.9. An equivalent damage spectrum has been formulated to minimise the number of load levels within the spectrum without compromising the amount of damage done to the blade structure. Results of fatigue testing indicate that predictions are close to the measured fatigue life of the blade. The stress distribution in fatigue critical areas of the blade during testing was found to be similar to the expected stress distribution under normal operational condition.