Design and development of low‐cost optical‐fiber sensors for temperature metrology: Process monitoring of an epoxy resin system

This article reports the design and deployment of two optical‐fiber temperature sensors based on the fiber Fabry–Perot etalon. The first involved the use of an extrinsic fiber Fabry–Perot sensor, but in this instance, the coefficient of thermal expansion of the reflector and/or capillary was chosen to offer a mismatch. Hence, the cavity length could increase or decrease according to the coefficient of thermal expansion of the fiber and/or capillary. For comparison, single‐mode and multimode optical‐fiber Bragg gratings were also used as temperature sensors. The Fabry–Perot sensors operated from ?50 to 410°C. The accuracy of the measurements was up to ±0.5°C with a low‐cost charged‐coupling‐device spectrometer. The sensors also worked effectively in a microwave oven and in a composite panel in an autoclave. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 83–95, 2004     

Process monitoring of a thermosetting resin using optical-fiber sensors in a microwave environment

Conventional means of curing thermosetting resins used in advanced fiber-reinforced composites involves heating the sample in an oven or autoclave where heat is transferred to the sample through conduction and convection. In general, the cure schedules that are used can be time consuming and expensive. Hence, significant attempts are being made to improve the processing efficiency and productivity of this class of material. Microwave-based processing has been claimed to offer the advantage of a significantly faster processing time. In this study, two remote (noncontact) sensor systems were designed and developed to facilitate spectral-based quantitative process monitoring inside a custom-modified commercial microwave oven. The two fiber-optic sensor systems were 1) a noncontact optical-fiber reflectance probe and 2) a reusable transmission probe assembly. Spectroscopic data were obtained using the fiber-optic probes at specified microwave power levels. Since conventional metal-based temperature monitoring devices cannot be used in the microwave oven, a low-cost disposable fiber-optic probe was developed. This design was based on an optical fiber-based extrinsic Fabry-Perot interferometer (FPI). The extrinsic FPI temperature sensor demonstrated an accuracy of /spl plusmn/0.5/spl deg/C over the range from ambient to 300/spl deg/C. The temperature of the resin system was also measured simultaneously, along with the spectral data, to monitor the progress of the chemical reaction (curing).     

Fiber optic sensors for noncontact process monitoring in a microwave environment

This article reports on the design and development of two fiber optic sensing systems that facilitate the cure monitoring of an epoxy/amine thermoset in a microwave oven. First, the design, construction, and evaluation of a fiber optic probe were necessary so that noncontact diffuse reflectance spectra could be obtained during the curing of the resin in a microwave oven. Second, a low‐cost, disposable fiber optic temperature sensor had to be developed for use in the microwave oven because the use of conventional metal‐based thermocouples was not possible. The deployment of the two sensor systems was demonstrated successfully. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3868–3873, 2003     

Comparison of the curing kinetics of the RTM6 epoxy resin system using differential scanning calorimetry and a microwave‐heated calorimeter

The cure of a commercial epoxy resin system, RTM6, was investigated using a conventional differential scanning calorimeter and a microwave‐heated calorimeter. Two curing methods, dynamic and isothermal, were carried out and the degree of cure and the reaction rates were compared. Several kinetics models ranging from a simple nth order model to more complicated models comprising nth order and autocatalytic kinetics models were used to describe the curing processes. The results showed that the resin cured isothermally showed similar cure times and final degree of cure using both conventional and microwave heating methods, suggesting similar curing mechanisms using both heating methods. The dynamic curing data were, however, different using two heating methods, possibly suggesting different curing mechanisms. Near‐infrared spectroscopy showed that in the dynamic curing of RTM6 using microwave heating, the epoxy‐amine reaction proceeded more rapidly than did the epoxy‐hydroxyl reaction. This was not the case during conventional curing of this resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3658–3668, 2006