Distributed Fiber Optic Strain Measurement Using Rayleigh Scatter in Composite Structures
This paper examines the implementation of distributed strain sensing to capture hundreds of simultaneous strain readings along the length of a 6.5 meter long glass fiber reinforced polymer (GFRP)
composite beam. In a collaborative effort with NC State University, a four point beam test was performed to failure.
This paper presents the use of distributed fiber optic sensing to achieve centimeter level resolution strain data along the entire length of a large composite beam. A 6.5 meter long composite beam, designed for use in a corrosive flue gas desulfurization (FGD) unit, was instrumented. A section of optical fiber was embedded into a fiberglass rope, which in turn was embedded into the composite beam during the manufacturing process. The beam was experimentally tested in four-point bending at the North Carolina State University Constructed Facilities Laboratory, and the strain profile along the entire length was measured using the embedded optical fiber. Strains of up to 6500 microstrain were measured at over 300 unique positions along the span by monitoring changes in the spectral shift of the Rayleigh scatter in the optical fiber using optical frequency domain reflectometry (OFDR). The fiber used in this test was optically equivalent to standard telecommunication fiber, allowing for low-cost, high-density strain measurements on large structures. The experiment confirms the potential of embedded fiber optic distributed sensing to be used for real-time health monitoring, or as a process feedback in an instrumented structural system. Benefits of employing distributed fiber optic sensing in structures such as the composite FGD unit include the ability to monitor and detect deterioration and damage, minimize the chance of unplanned downtime or failure, and limit exposure to consequences such as environmental contamination.
E. Sanborn et al., “Distributed Fiber Optic Strain Measurement using Rayleigh Scatter in Composite Structures”, SEM Conf., Montville, CT, June 2011, Vol. 6