Interaction between optical fibre sensors and matrix cracks in cross-ply GFRP laminates. Part 2: Crack detection

Polarimetric optical fibre sensors have been embedded within the 0° ply and close to the 0°/90° interface of transparent cross-ply GFRP coupons. The coupons have been subjected to an increasing quasi-static load so that transverse ply cracks initiate and propagate across the coupon. Crack accumulation has been monitored using the optical output signal from the polarimetric sensor, strain measurements from a long gauge-length extensometer, load recordings during the test and by video recording of crack development. These combined observations have enabled a direct correlation to be made between matrix crack growth past the sensor and a step-change in the sensor response. The use of band-pass FFT filtering has demonstrated that such cracks could be detected in real time.