Free-form fabrication of composites with embedded sensors

Layerwise processing methods allow parts to be built with sensors placed within the structure and fully embedded. Blocks of epoxy resin have been formed with embedded optical fibers. The fiber can be used to monitor curing and water uptake of the epoxy using ambient light which passes through the resin, is collected by the fiber and analyzed in a near-IR spectrometer. Piezoelectric polymer films have also been embedded in epoxy and used to monitor curing by changes in response to an external stress pulse. In the long run, it would be desirable to form parts containing many sensors with sensitivity differing environmental variables. Epoxy parts have been freeformed with lines of conducting carbon-filled polymer written into the structure during forming. Where they are at the surface of the part, these materials respond to solvent exposure by a resistance change. Parts have been made with sensors distributed across the surface and their ability to sense gradients of solvent vapor, and so direction to a source, is being tested.