It is generally appreciated that the ingress of moisture in composites can have adverse effects on matrix-dominated properties such as the glass transition temperature and compressive mechanical properties. Moisture ingress in composites can also lead to swelling and blistering. A number of excellent studies have been reported on the detection, modelling and effects of moisture ingress on the properties of thermosetting resins (matrix) and composites. However, it is generally taken for granted that the quality of the resin and the processing conditions used to cross-link the resin are identical.
Given the recent advances in the design and deployment of optical-fibre sensors in composites, it is now possible to use the same sensor to facilitate in-situ cure monitoring and structural health monitoring (after processing). This paper will present recent developments in the design of low-cost fibre-optic sensor systems for in-situ chemical process monitoring and the detection of moisture ingress after curing. The cure kinetics derived from three fibre optic sensor designs is presented as well as those obtained from evanescent-wave spectroscopy using E-glass fibres. After conducting the in-situ cure monitoring experiments, one of the fibre-optic sensor designs was selected and the samples (with the embedded sensors) were dried to constant mass at 50°C then transferred to water baths maintained at 70, 50, and 30 °C. The diffusion kinetics for the samples was determined using samples without and with embedded optical-fibre sensors.
The effect of moisture ingress in the resin was also assessed using dynamic mechanical thermal analysis (DMTA), transmission infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Preliminary results are also presented to demonstrate that the reinforcing fibres in E-glass composites can be used to track the cross-linking kinetics of a commercial epoxy/amine resin is presented.
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Mahendran, R., Chen, R., Wang, L., Pandita, S.D., Machavaram, V.R., Kukureka, S.N. and Fernando, G.F., 2008, March. Chemical process monitoring and the detection of moisture ingress in composites. In The 15th International Symposium on: Smart Structures and Materials & Nondestructive Evaluation and Health Monitoring (pp. 69330R-69330R). International Society for Optics and Photonics.
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