Fiber Optic Sensor Development for Real-Time In-Situ Epoxy Cure Monitoring

Abstract

Analysis of a new fiber optic sensor based on the principle of Fresnel reflection is presented in order to develop a robust, flexible, readily embedded, high sensitivity and low-cost cure monitoring tool for intelligent control of composite manufacturing. This approach is distinct from previous work on on-line in-situ monitoring sensors in that the transducer is simply the fiber optic/epoxy interface. This leads to a more simple, less intrusive, and lower cost sensing system. The response of the sensor is a function of the mismatch in refractive index between the fiber optic end/resin interface. The refractive index of the resin is a nonlinear function of the temperature and the cure reaction of the resin. The sensing system detects the mismatch in the refractive index and generates a characteristic profile that gives the chemorheological information about the curing resin. Under isothermal cure conditions, the effect of the temperature on the refractive index mismatch can be eliminated. In this situation, the optical response of the sensor is only dependent on the cure kinetics and the state of the cross-linking in the material. A calibration method has been developed to interpret the optical response directly as the degree-of-cure of the resin. This work provides analysis of the fundamental sensor response and correlates it to the material state (degree-of-cure). These results provide a basis for extending the use of this sensor technology for on-line real-time cure monitoring and control.

Monitoring the resin infusion manufacturing process under industrial environment using distributed sensors

“…A temperature peak can be observed at the beginning of zone 3. The zone between the beginning and the end of this peak corresponds to the increasing reflected light intensity, which relates to the density of the resin, according to Equation 2 [24]. During this stage, the liquid resin is transformed into a solid through an exothermal reaction; it involves an increase of resin density.…”

A Fresnel's Reflection Optical Fiber Sensor for Thermoset Polymer Cure Monitoring

“…Due to its low intrusivity, this sensor can be easily embedded into a composite material to monitor the resin cure in-situ. 3 , Torsional Braid Analysis (TBA) 7 or ultrasonic techniques 2,8 ; • measurement of optical properties by using Fourier Transform Infrared (FTIR) spectroscopy 9,10 , Raman Spectroscopy 11 , Fiber Bragg Gratings (FBG) 12 and Fresnel' reflection based sensors 13,14,15,16 .…”

Anisothermal thermosetting resin cure monitored by optical fiber refractometer

“…Its intensity depends directly on the resin refractive index. This technique has been demonstrated to be relevant to monitor the evolution of the cure processing . Drawbacks come from the facts that this technique needs to be externally calibrated to give quantitative results and is not totally reproducible as the reflection coefficient depends on the quality of the optical fiber end cleavage.…”

“…Indeed, the quality of the composite part depends on the control of the process cycle and its parameters (temperature, pressure/vacuum, curing time). In order to improve the curing of thermosetting resins and therefore the quality and reliability of these composite parts, high performance in situ sensing systems are required for the monitoring of processes .…”