Cure Process Monitoring for Carbon Fiber/Epoxy Composite Laminates Using Tilted FBG Sensors

Tilted Fiber Bragg Grating (TFBG) sensors is an optical fiber sensor with a diffraction grating tilted small angle. TFBG sensors has Bragg resonance, the ghost mode resonance and the cladding mode resonance. It is known that strain and refractive index (RI) can be measured individually analyzing appropriately these resonances. The RI corresponds to degree of cure of epoxy resin, hence TFBG sensors is expected to apply to cure process monitoring of carbon/epoxy laminates and epoxy film adhesive. However, simultaneous measurement of strain and RI has not been established, and a TFBG sensor has not been applied to cure process monitoring of carbon/epoxy laminates. This study demonstrated the applicability of the TFBG sensor for cure process monitoring of carbon/epoxy laminates. Firstly, a simultaneous measurement method of strain and RI was developed by using the TFBG sensor. by using a simultaneous measurement method, RI and strain in curing process monitoring of carbon/epoxy laminates were measured. As a result, the RI due to curing of carbon/epoxy laminates were successfully measured by using the cladding mode. The strain due to thermal expansion and shrinkage could be measured by using the Bragg resonance. Thus, the TFBG sensor is useful to measure RI and strain in cure process monitoring of carbon/epoxy laminates.