Damage detection by using experimental modal analysis technique and fiber Bragg gratings

In this work, the application of fiber Bragg gratings (FBGs) to damage detection tests is reported. The presence of alterations on a mechanical structure can be evaluated from variations of the resonances (frequency and amplitudes) of its frequency response function (FRF). This latter can be evaluated through experimental approaches, like the modal analysis, involving mechanical excitation systems (instrumented hammers and piezoelectric elements) and adequate sensing systems. Here, results of preliminary tests performed with FBGs externally bonded on a simply steel structure are reported. FBG sensors have been interrogated with a low cost passive technique based on optical filtering As previous step, in order to test FBGs capability to retrieve the dynamic features of a test sample in a wide frequency range, results of high frequency (1.5kHz) modal analysis tests are reported. In both cases, L e. modal analysis and damage detection tests respectively, laser Doppler vibrometers and accelerometers, representative of the state of the art for this application field, have been used as reference sensors. As future work, an algorithm to quantify the damage level of a structure from experimental data will be determined.