Quantitative investigation in distributed sensing of structural defects with Brillouin optical time domain reflectometry

Abstract

Distributed sensing offers great promise in structural health monitoring of bridges and other types of critical structures. Over the years, a number of different Brillouin scattering–based systems have been developed for distributed sensing, including sensors based on the Brillouin optical time domain reflectometer. This study pertains to the quantitative characterization of Brillouin optical time domain reflectometer–based sensors for monitoring of distributed strains and detection of defects. This study involved experiments involving a 15-m-long beam and simulated defects. In the experiments, the effect of strain localization at the defect sites was masked by the low spatial resolution of the Brillouin optical time domain reflectometer. The Brillouin optical time domain reflectometer–measured response was evaluated by numerical modeling of the beam. Computation of the flexural strains involved a hybrid approach in which the experimentally determined degraded stiffnesses of the defect zones were employed in the finite element model. Unlike the Brillouin optical time domain reflectometer–measured strains, finite element model analysis of the beam indicated formation of sharp peaks in the strain distributions at the locations of the defects. The effects of these measurement errors were numerically quantified by separating them from the influence of the spatial resolution errors.