Initial defects, for example, those occurring during the production of a rotor blade, encourage early damages such as rain erosion at the leading edge of wind turbine rotor blades. To investigate the potential that initial defects have for early damage, long-pulse thermography as a non-destructive and contactless measurement technique is applied to a strongly curved and coated test specimen for the first time. This specimen is similar in structural size and design to a rotor blade leading edge and introduced with sub-surface defects whose diameters range between 2mm and 3.5mm at depths between 1.5mm and 2.5mm below the surface. On the curved and coated test specimen, sub-surface defects with a depth-to-diameter ratio of up to 1.04 are successfully detected. In particular, defects are also detectable when being observed from a non-perpendicular viewing angle, where the intensity of the defects decreases with increasing viewing angle due to the strong surface curvature. In conclusion, long-pulse thermography is suitable for the detection of sub-surface defects on coated and curved components and is therefore a promising technique for the on-site application during inspection of rotor blade leading edges.
Zusammenfassung Zum Umformen großer Bleche in kleinen Stückzahlen stellt die inkrementelle Blechumformung eine wirtschaftliche Alternative zum Tiefziehen dar. Auftretende Werkzeugablenkungen führen jedoch zu erhöhten Formabweichungen. Mit einer von der Maschinenkinematik unabhängigen In-Prozess-Messung der Werkzeugablenkung könnten diese kompensiert und somit die geometrischen Abweichungen minimiert werden. Deshalb wird ein optisches Multi-Sensorsystem konzipiert, um eine berührungslose Messung der Werkzeugposition mit der geforderten Messunsicherheit von 15 µm in einem Messabstand bis 2 m zu ermöglichen. Das Sensorsystemkonzept sieht eine Vielzahl preiswerter Sensoren vor, die jeweils einen Winkel zu einer Punktlichtquelle am Werkzeug erfassen. Basierend auf den gemessenen Winkeln aller zueinander kalibrierten Sensoren lässt sich die Position des Werkzeugs im dreidimensionalen Fertigungsvolumen per Multiangulation berechnen. Die mit dem Gesamtsystem erreichbare Messunsicherheit wurde mittels einer experimentellen Charakterisierung eines realisierten Angulationssensors sowie einer Unsicherheitsfortpflanzung abgeschätzt. Im Ergebnis erfüllt das Multi-Sensorkonzept sämtliche Anforderungen an die In-Prozess-Messung der Werkzeugablenkung bei der inkrementellen Blechumformung.
To validate design guidelines of bionic, holistic lightweight gears with integrated load monitoring, an inside sensor system will be used to continuously record the deformation behavior under dynamic load. Strain gauges based on thin-film technology and metal substrate are used as sensors for this purpose. Measurements on a gear show that, during the entire tooth meshing, the deformation behavior of each tooth can continuously be measured with the implemented inside sensor system and that the various tooth meshing zones can also be detected.
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