Soundness of wind turbine blade plays paramount role in supplying cheap and reliable wind energy. To ensure that blades are sound and free from inherent manufacturing defects, easy and reliable quality evaluation before delivering blades for installation is crucial. We propose an ultrasonic amplitude imaging method based on Ultrasonic Propagation Imaging (UPI) system for this purpose. The system utilizes a scanning Q-switched continuous wave laser as ultrasonic wave generator. Various acousto-ultrasonic sensors, either contact or non-contact type, could be adopted as ultrasonic receiver. The system was tested on a blade section made of glass fiber reinforced plastic sandwiched with balsa wood. The leading edge of the specimen with a kissing disbond was inspected. A PZT-based sensor attached temporarily on the outer surface of a blade was used for ultrasonic reception to demonstrate that this imaging method is applicable even for the blades without integrated sensor. The amplitude map clearly showed the disbond defect with the kissing features. The location, shape, and size of the defect evaluated from the result agree excellently with the actual defect. The result proved that the proposed method works well for the quality evaluation of wind turbine blades. Inheriting the advantages of UPI technology, i.e. focusing-free characteristics, acceptance of large laser incident angle up to 60°, and rapid scanning without needing an expensive scan gantry, this system is suitable for automatic quality evaluation of blades with different geometry. On top of that, this system does not require any reference data, making it a flexible quality evaluation system suitable for different methods of blade production flow.
Non-destructive evaluation (NDE) and structural health management (SHM) with the ability to evaluate the severity of a damage are important to ensure the reliability of a structure. We propose a local non-destructive evaluation (NDE) system based on Anomalous Wave Propagation Imaging (AWPI) method. When possible damage is flagged during the lifecycle of the structure, the proposed system will be launched for automatic damage evaluation. This technology was demonstrated on a CFRP skin-spar-stringers wingbox integrated with an AE sensor. 17 mm diameter impact damage was made between the stringers using hammer strike from outer surface of the skin. Based on the impact location determined by other global structural health monitoring system, the AWPI automatically inspects an area 400×400 mm2 with the impacted location enclosed. Anomalous Wave Propagation Movie (AWPM) was generated as inspection result. As contrast to its predecessor, the AWPM shows only the damage induced ultrasonic wave (anomalous wave), making the damage detection an intuitive decision making process. Precise damage localization was performed by identifying the location of area with anomalous wave propagation in the AWPM. Besides, the size of the area with anomalous wave agreed well with the size of impact damage, which demonstrated that damage size quantification is possible using the proposed system. Being sensitive only to anomalous wave, it is expected that this NDE system is exceptionally suitable not only for aircraft structures such as wingbox with stiffeners, but also for other complex engineering structures.
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