Monitoring local strains in cracked cross-ply composites using an embedded aramid fibre strain sensor

Single aramid fibre strain sensors have been embedded in transparent glass-fibre reinforced epoxy resin cross-ply laminates. The sensors, located at the 0 degrees/90 degrees/0 degrees ply interfaces, were interrogated by a remote laser Raman microprobe which enabled the changes in the longitudinal strain in the 0 degrees plies caused by-transverse cracking in the 90 degrees ply to be monitored. Strain magnifications of up to about 6 were measured in the crack plane, 10 mu m from the 0 degrees/90 degrees ply interface, and it is estimated that the region of enhanced strain extends to a distance of about 40 mu m from the interface. Crack interactions were seen to occur for crack spacings of less than two transverse ply thicknesses. (C) 1998 Kluwer Academic Publishers.