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Wind turbines are gaining importance in the last years because of their high efficiency during energy production without greenhouse gas emission. Furthermore, they can be installed both on-and off-shore. However, wind blade maintenance operations have become difficult and expensive due basically to size aspects and operative costs related with their location and out-off service period. A non-destructive technique capable of detecting most significant in service defects in composite wind blade is infrared thermography (IRT). However, this method can only be applied by developing cost efficient in situ inspection strategies. This work presents a feasibility study for defect detection during maintenance operations in wind blades using unmanned aerial systems (UASs). IRT inspections are performed by means of passive IRT methodology first (i) for specimen located at the ground level with artificial defects (like delaminations, cracks, impact damage and debondings) and later (ii) during flight operation using an rotorcraft UAS. The developed inspection strategies, test results and several features of the developed acquisition system are reported.

The starting materials are high purity metals: Zr (99.6 %), Cu (99.999 %), Al (99.999 %), Nb (99.995 %), and Ni (99.995 %). Two steps are used for the preparation of master alloys. First, the binary solid-solution ingots of Zr-Nb are fabricated. Second, Zr-Nb ingots are arc melted into master alloy with the remaining elemental components, such as Ni, Cu, and Al. For each step, the ingot is melted and flipped 5 times for total about 8 min. Then, the bulk metallic glass of the nominal composition of (Zr 58 Ni 13.6 Cu 18 Al 10.4 ) 99 Nb 1 with the length, width, and thickness of 75 mm × 6 mm × 2 mm was fabricated by suction casting the alloy into copper mold under a Ti-gettered Ar atmosphere. The structure was examined by X-ray diffraction (XRD) with Cu Ka radiation and the high-resolution-transmission-electron microscopy (HRTEM). The thin film for HRTEM is obtained by twin-injection. The crystallization and melting process was given by differential thermal analysis (DTA). The crystallization kinetics of the metallic glass was characterized by continuous and isothermal heating, using DSC (Perkin-Elmer DSC-7). In the case of continuous heating, a set of DSC curves were recorded at heating rates of 30, 40, 50, and 60 K/min. For the isothermal analysis, the metallic glasses were firstly heated to a fixed temperature (723, 733, 743, 753, and 763 K) at a rate of 200 K/min., and, then, held for a certain period of time until the completion of crystallization. The DSC system was calibrated for the temperature by using zinc and indium standards, giving an accuracy of ± 0.02 K. The DSC data were processed using the laboratory-edited computer program. Fig. 4. 3D reconstruction of the eutectic Si in AlSi7Sr: a) whole studied region; b) union of three different grains (presented by different grey-scales of Si in each grain); c) three different grains showing Si fibres of different thickness.Fig. 5. 3D reconstruction of lamellar Si in unmodified AlSi7 for a,b) the whole studied region at different observation angle and c) connecting nodes.

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