In-Situ Composite Cure Monitor and In-Service Strain Sensor

Fiber and Sensor Technologies, Inc. proposes to develop a fiber optic sensor that can be embedded in a polymeric matrix composite to monitor the state of the composite "from cradle to grave". During fabrication, the sensor will output quantitative data which will indicate the degree of polymerization of the matrix resin. In service, the same sensor will monitor internal strains of the composite part. Continuous monitoring of the sensor output can be used to detect strains that may preface failure of the component. Two technical approaches will be experimentally compared, to select the most promising for Phase II commercialization. In the first, a modified extrinsic Fabry-Perot interferometric (EFPI) fiber optic strain sensor will be configured to measure directly the viscosity of the matrix, from which the cure state may be derived. By coating the sensor with an actuator (such as a magnetostrictive material), the embedded sensor can be made to vibrate under appropriate excitation. The optical sensor will measure the mechanical response of the sensor, which will depend on the viscolastic properties of the matrix. In the second approach, an embedded EFPI sensor will be used to correlate changes in the refractive index of the epoxy with cure state.