Fibre-optic strain measurement for structural integrity monitoring

The use of a fiber-optic strain measurement system to monitor the in-plane strain distribution in a large structure is proposed. A fiber is zigzagged over the structure and when the structure is strained the fiber is bent and the strain distribution is then measured by analyzing the backscatter waveforms with an Optical Time Domain Reflectometer (OTDR). The OTDR used in the experiment, which measures with a resolution of 0.005 dB and a spatial resolution of 0.25 m, is described. The application of this technique reveals that the sensitivity can be tuned by varying the spacing and amplitude diameter of the zigzagged fiber; a mean strain of over 0.25 m can be measured with a resolution of 100 microstrain.