The effects of thermal strain, permanent strain and mechanical fatigue on strain-sensing fiber optic cable

摘要

The objective of this research is to validate the strain-sensing capability of fiber optic cable. In contrast to traditional point-measurement sensors, this distributed strain and temperature (DST) cable provides continuous data along its length. As the cable strains mechanically or thermally, the Brillouin frequency changes and can be mathematically correlated with strain. The mechanical strain validation setup holds a 3.5-meter long cable between proprietary end clamps that allow fine changes in cable length, which are measured with a digital caliper. The caliper-measured strain and Omnisens-measured strain plot as parallel straight lines, indicating no slip between the fiber and the cable's outer layers. The strain values are also validated using strain gages attached to the DST. Readings of successive tests on individual cables are plotted to investigate mechanical fatigue and permanent strain. The thermal strain validation setup consists of a 3-meter long DST cable immersed in water. The water temperature is changed incrementally and temperatures are recorded using a thermocouple immersed in the water. The Omnisens system is used to determine the change in Brillouin frequency with temperature.