Acousto-ultrasonics for wind turbine blade inspection
Although wind is currently the most promising renewable energy source and wind turbines the widespread means of harnessing wind energy, there are difficulties to overcome. Despite the use of advanced composite materials, turbine rotor blades continue to fail due to highly variable loads. Defects in fibre-reinforced composites cannot be unambiguously matched with specific mechanical properties, making traditional non-destructive testing inadequate. However, researchers have now introduced an autonomous robotic system to solve the problem. With EU support of the project AUTOWINSPEC (Automated mechanical property and fatigue life assessment of composite wind turbine blades in less than 4 hours), they developed non-destructive testing technology based on acousto-ultrasonics (AU) to reliably evaluate the integrity of rotor blades. AU combines acoustic emission monitoring produced by induced stress waves with ultrasonic characterisation of the properties of the material between the source and the receiver. The robotic climbing mechanism fitted with AU technology can be deployed even by an untrained operator. The robotic ring-like mechanism climbs using ropes and attaches on turbine blades using wheels. AU inspection is performed by transducers and receivers placed on the outside of the wheels. AUTOWINSPEC researchers have estimated that the whole procedure is completed in less than four hours. Afterwards, using advanced signal analysis and pattern recognition, a map of the blade is produced, where areas of poor mechanical properties are depicted with millimetre resolution. In addition, an estimate of the remaining lifetime of the blade is provided. The AUTOWINSPEC system is expected to cut wind turbine blade maintenance costs by 84 % and time in half, while eliminating the danger of rope access as well as reducing downtime. Project small and medium-sized enterprises will improve their competitive position in the EU wind turbine maintenance market, set to reach EUR 42 billion by 2020.
Keywords
Acousto-ultrasonics, wind turbine blade, renewable energy, non-destructive testing, AUTOWINSPEC
