Investigation of the transient behavior of a cantilever using a point-wise fiber Bragg gratingdisplacement sensor system

Abstract

This paper presents a fiber Bragg grating (FBG) sensor system setup method to measurethe transient response of dynamic displacement for a cantilever subjected to impactloadings. An LPFG filter-based wavelength–optical intensity modulation technique is usedin this study. The transient responses of particle motions measured by an FBGdisplacement sensor are compared with those obtained simultaneously by a laser Dopplervibrometer (LDV). The resonant frequencies of the cantilever are determined byemploying a fast Fourier transform on the transient displacement responses obtainedfrom the FBG and the LDV. An optical full-field measurement technique calledamplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) is also usedto provide the full-field vibration mode shapes and resonant frequencies of thecantilever. The resonant frequencies obtained from four experimental measurementtechniques, i.e., FBG, LDV, AF-ESPI, and shaker, are compared with those predictedfrom theoretical and FEM numerical calculations. Furthermore, the amplitudeof the frequency spectra obtained from the FBG and the LDV are emphasizedfrom the mode shapes and impact locations of the steel ball. The proposed FBGdisplacement sensor is proved to be able to measure transient point-wise displacementresponses which can also be used to determine the resonant frequencies of structures.