Micromechanics of optical fiber sensors embedded in laminated smart structures

The mechanical interaction between an embedded optical fiber sensor and its host laminated composite is investigated with a combination of moire interferometry and Fourier transform fringe interpretation. Moire interferometry alone lacks the spatial resolution required to provide the detailed strain analysis in the region of the optical fiber. However, the combination of the two methods has proved very powerful. Spatial resolutions on the order of 2 microns are achieved with monocular magnification using conventional optics. Results are presented for a 600-micron dual coated and a 250-micron single coated optical fiber embedded at the mid-plane of a 90 sub 12 graphite/epoxy laminated composite compression specimen. Perturbation strain fields caused by the 600-micron embedded optical fiber are provided and the residual strains, which are commonly developed for these material systems and loading are presented for the 250-micron fiber diameter specimen.