Point-strain measurement within laminated fiber composite materials

This paper reports the development of a `smart' strain monitor based upon the use of resonant Raman spectroscopy to monitor point strain, potentially in-flight, within laminated carbon fiber composite aircraft structures. The DCH-polydiacetylene fiber together with an optic fiber as the light guide are embedded in the carbon fiber composite laminate as the strain sensor. The DCH-polydiacetylene fibers are single crystal fibers, whose Raman spectra are resonantly enhanced when excited by the red laser light. The Raman frequencies of the DCH fiber are observed to shift linearly to lower frequency with applied uniaxial strain.