In order to help increase wind turbine efficiency, the Fraunhofer Institute for Applied Solid State Physics IAF has developed an innovative radar scanner that can detect defects in composite wind turbine blades with more accuracy. By visualizing the defects in a cross-sectional view, customers can save costs on production and operation.
As Fraunhofer explains, modern wind turbine blades are mainly constructed from glass fiber and carbon fiber reinforced plastics so that they can elastically absorb the wind energy from strong gusts without breaking. For a single blade, up to 100 sheets of glass fiber webbing are layered on top of each other, shaped and then glued together with epoxy resin.
“The difficulty lies in layering the glass fiber sheets flat before they are glued, without creating undulations and folds, and avoiding the formation of lumps of resin or sections of laminate which don’t set when applying the epoxy,” explains Dr. Axel Hülsmann, coordinator of the radar project and group manager of sensor systems at the Fraunhofer IAF.
These kinds of defects, as well as delaminations or fractures, can be identified on a large-scale using infrared thermography. Quality control is essential, and that’s where their scanner comes in.
“Our material scanner enables defects to be identified with even greater accuracy, as depth resolution is also possible with radar technology – even in places where ultrasound methods fail,” says Hülsmann.
At the core of the material scanner is a high-frequency radar, which operates with only very few watts of transmitting power. Specialized software is used to process the transmitter and receiver signals and visualize the measurement results.
“This enables us to generate a cross-sectional view of the blade, in which defects can be identified in the millimeter range, and makes our material scanner significantly more accurate than conventional methods,” says Hülsmann.
The radar module is extremely light and compact thanks to its construction, in which different components and functions are integrated into a single chip. Measuring 42 x 28 x 79 mm, it is approximately the size of a pack of cigarettes and only weighs 160 grams.
Fraunhofer adds that in the future, the material scanner could also be used for maintenance, where it could classify defects themselves. It could also be used to contribute to the development of innovative material inspections in aircraft, such as the composites-intensive Boeing 787 Dreamliner or the Airbus A350 aircraft.
The Fraunhofer IAF will be introducing the material scanner for testing wind turbine blades at the Baden-Württemberg booth at the Hannover Messe show later this month.