Embedded Optical Fiber Strain Sensor For Composite Structure Applications

Optical fibers have been embedded in polymer-matrix fiber reinforced composite materials during fabrication. Subsequent testing has shown that optical coupling to, and transmission through, the embedded fibers can be accomplished. A radio frequency interferometric sensor instrument has been built to detect small changes in the optical fiber path length. Elongations smaller than 1 mm over a 1 m path, corresponding to a distributed strain threshold below 1000 μin./in., have been detected. The instrument has been used to demonstrate strain measurement with embedded fibers in graphite/epoxy test specimens. These measurements are compared with electrical resistance strain gage readings.