Impact Loading and Damage Detection in a Carbon Composite TX-100 Wind Turbine Rotor Blade

An experimental 9-m composite rotor blade with integrated carbon-carbon features and an outer fiber direction of 20o was fatigued to failure. The blade initially developed a crack at 65o on the high pressure side near the 4.6-m station at 2.5 M cycles and the crack then coalesced to the 20o fiber direction until the test was stopped at 4 M cycles. An array of highsensitivity triaxial accelerometers, low-frequency capacitive accelerometers, and piezoelectric actuators with force sensors was distributed over the surface of the blade to monitor the loading and blade damage. A triaxial accelerometer at the tip was used to measure the tip deflection in the flap, lead-lag, and root-tip directions throughout the test. In-plane displacement measurements between the damage and the root were found to be sensitive to the crack growth and direction. The dynamic features of the rotor blade were sensitive to the variation in ambient temperature. Active diagnostics with the method of virtual forces was sensitive to the damage for in-plane measurements following adjustment for thermal effects. Impact identification was demonstrated with 93% accuracy of the location and within 1.3% accuracy of the magnitude. Modal filtering provided a means of monitoring the fatigue loading in near-real time. Second-order harmonics excited by the fatigue system were shown to exist at the tip in the lead-lag and root-tip directions. Findings of this test will be instrumental in future development of accelerometer-based wind turbine rotor blade monitoring.