In aircraft structures, FBG sensors are mostly used to monitor fuselage parts, aircraft cockpit or composite wings. At present, FBG sensors are integral parts of the SHM systems installed on different structures: bridges, offshore platforms, buildings, marine vessels. FBG sensors can be mounted on structure surfaces, as well as embedded into the material during its manufacturing. The most important advantages of FBG sensors are their small size, high multiplexing capabilities, corrosion resistance, and lack of calibration needs. In SHM systems, FBG sensors are mostly applied for strain, and temperature measurements. Fibre Bragg grating (FBG) sensors are a very interesting tool for SHM applications. The high complexity and costs of aircraft structures, combined with their high operational reliability and safety needs, result in an increasing interest in Structural Health Monitoring (SHM) systems. It was confirmed that the proposed signal processing method, based on spectrogram analyses, can be applied for the detection of fatigue crack development in metal structures. Additionally, spectrogram-based analyses were performed, focused on the acoustic waves phenomena related to a crack propagation process. The strain values and the natural frequencies of the sample that were determined experimentally were compared with the values achieved from the finite element method model, with both methods showing good agreement. However, the strain curves were almost insensitive to the crack propagation process, except in the last stage of the test, when the crack length was equal to 25 mm. It was observed that the strain curves determined by the FBG sensors agreed well with the fatigue force profile. During the fatigue test, the sample was equipped with FBG sensors applied for strain measurement and the vibration-based strain monitoring.
The investigations were carried out on an aluminium alloy sample (a part of the Mi-2 helicopter rotor blade).
The paper presents the analysis of the possibility of fatigue crack detection and monitoring its propagation process using fibre Bragg grating (FBG) sensors.
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