Long-gage optical fiber extensometers for dynamic evaluation of structures

This paper deals with the study of the capacity of continuously attached long-gage fiber optic sensors for a new use: dynamic evaluation of structures. The optical system is first presented, followed by the development of the precise formulation of the measurement data obtained by this sensor when applied to the dynamic analysis of beams, especially under bending oscillations. This sensor allows us to find the curvature mode shapes. Numerical simulations are then performed to estimate the dynamic characteristics of the beam by means of the continuous wavelet transform, using the data obtained with this sensor. Finally, the fiber optic sensors are bonded on a real cantilever beam and experimental data are collected from the optical measurement system, in the case of aftershock free oscillations of the instrumented beam. A similar modal identification procedure as that proposed for numerical simulations is used and the results are compared to those obtained with accelerometers and long strain gauges. This type of sensor, allowing us to find the curvature mode shapes, will be a good candidate for damage detection.