PSI - Issue 68

Hugo Mesquita Vasconcelos et al. / Procedia Structural Integrity 68 (2025) 795–801 Hugo Mesquita Vasconcelos et al. / Structural Integrity Procedia 00 (2025) 000–000

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Keywords: Thermographic Inspection, Structural Integrity, UAV, wind turbine blades.

1. Introduction Wind energy plays a crucial role in global energy, contributing significantly to sustainable power generation. As of recent statistics, approximately 20% of Europe's power consumption is sourced from wind energy, with projections by the EU Commission indicating that by 2050, this figure could rise to 50%, a milestone already achieved by Denmark. The reliance on wind power underscores its importance, yet it brings to light the challenges associated with ageing infrastructure. Wind farms built during the early phases of this energy shift are now approaching the end of their operational life. Given the size of these turbines, maintaining their structural integrity is of utmost importance to ensure both safety and efficiency (Kramer et al. 2024; WindEurope 2024). The conventional maintenance protocols for wind turbines, in Portugal, predominantly focus on significant transmission components, often neglecting the blades until evident issues arise. Typically, structural assessments of the blades are conducted visually or audibly by maintenance personnel from the ground. This method, while straightforward, overlooks smaller yet critical anomalies that could compromise the turbine's functionality. Consequently, there is a pressing need for a more comprehensive approach to assess the entire blade's structural integrity, minimising downtime and enhancing safety (Nejad, Gao, and Moan 2014). Thermography, a non-destructive testing technique, involves the detection and analysis of infrared radiation emitted from an object, which correlates with its temperature. The produced thermal images offer a visual representation of the thermal distribution across the component. Literature on thermography primarily focuses on ground-based applications or examinations of small segments of turbine blades. Studies have demonstrated its effectiveness in identifying defects in controlled environments, but its application using UAVs in the field introduces a new dimension. This adaptation is particularly beneficial for turbines located in offshore or hard-to-access areas, where traditional inspection methods are logistically challenging and costly (Sanati, Wood, and Sun 2018). In response to these challenges, the development of an innovative non-destructive inspection strategy using thermographic analysis has been proposed and validated. This technique employs unmanned aerial vehicles (UAVs) equipped with microbolometer-based cameras to capture thermal imagery of the wind turbine blade under different thermal conditions.

Nomenclature EU

European Union UAV Unmanned aerial vehicles

2. Methodology The methodology employed in this study involves a two-step thermographic imaging process designed to assess the structural integrity of wind turbine blades by capturing thermal discrepancies that indicate potential defects. The initial step consists of acquiring a thermographic image early in the morning when the turbine blade is at its coldest due to minimal solar heating overnight. This image serves as a baseline reference, capturing the natural thermal state of the blade without the influence of external heating factors. Subsequently, a second thermographic image is captured around noon when the sun is at its zenith, ensuring the blade is near its maximum temperature due to solar exposure. This timing is critical as it maximizes the thermal gradient between defective and non-defective areas of the blade. Defects within the blade, such as voids or delaminations, typically exhibit different thermal properties compared to the unaffected areas. These discrepancies are due to variations in thermal conductivity and capacity, causing defective regions to heat up or cool down at different rates than their surrounding materials.