Miniature Fiber Optic Viscoelasticity Sensor for Composite Cure Monitoring

The most promising strategy for reducing the cost of manufacturing polymer matrix composites while improving their reliability is the use of sensors during processing to permit control of the cure cycle based on measurements of the material's internal state. While sensors have been demonstrated that infer the material state indirectly through measurements of acoustic impedance, electrical impedance, or refractive index, sensors that directly measure parameters critical to composite manufacturing, such as resin rheology and resin hydrostatic pressure, would improve characterization of thermoset resins during cure. Here we describe the development of a multifunctional fiber optic sensor that may be embedded in a composite part during lay-up to monitor the state of the polymer matrix during processing. This sensor will output quantitative data which will indicate the viscoelasticity of the thermoset matrix resin. The same sensor will additionally function as a strain sensor following fabrication, capable of monitoring residual strains due to manufacturing or in-service internal strains.