Cure and viscosity measurement of thermosetting epoxy resin with fresnel reflectometer sensors

Fibre optic sensors are suitable for process monitoring because they are versatile and provide a way to overcome the size and material limitations of electrical sensors. Earlier research results show that fibre optic sensors and measurement systems are capable of measuring a variety of process parameters. Two sensor types stick out at this: Fibre Bragg grating sensors (FBG) and Fresnel sensors. Dual-sensing fibre optic sensor systems exploiting the versatile nature of these sensors are not available. However, most commercial FBG interrogators are equipped with the required hardware to also interrogate Fresnel sensors. Therefore, it is investigated whether this sensing scheme is able to measure the degree of curing and the viscosity of thermosetting epoxy resin during curing with Fresnel sensors. For that reason, the refractive index measurement uncertainty of said sensing scheme was investigated. Moreover, the degree of cure and viscosity of curing resin was correlated with its refractive index under isothermal and non-isothermal conditions to deduct analytical models for both parameters. This thesis describes the method to measure the refractive index with Fresnel sensors in combination with an FBG interrogator and it describes the applied calibration procedure. Additionally, two models are proposed to measure the degree of cure and the viscosity of curing thermosetting epoxy resin based on its resin refractive index and temperature; and their application is presented during composite manufacturing. The observed refractive index measurement uncertainty is sufficiently low to measure curing of thermosetting epoxy resins typical to composite manufacturing. Further, it was found that the proposed models reproduce curing and viscosity behaviour well. This shows that the FBG interrogator is suitable to interrogate Fresnel sensors for cure monitoring during composite manufacturing. This ability opens new possibilities for process monitoring of composite manufacturing.