| Conservative and costly cure cycles for processing thermoset composites currently used in aerospace industries ensure that parts are completely cured regardless of the materials used in different parts in a batch and locations of parts cured in an autoclave. Cure cycle optimization is therefore expected to reduce the processing time while maintaining the part quality in order to improve the productive efficiency and reduce the production cost. Material parameters, such as viscosity, gel point, degree of cure, residual strain/stress and modulus, are required to be monitored to control the cure procedure and ensure final part quality. Reliable sensors that can measure these properties of interest accurately and quickly are required for on-line optimization of cure cycles. The objective of this thesis was to evaluate the suitability of the most prospective sensors available in the market that have the potential for use in on-line monitoring of curing process, including the ultrasonic sensor, dielectric sensor, and fiber Bragg grating sensor. A processing mold was designed and fabricated to simulate the autoclave processing environment. Sensors were tested during different cure cycles using both the neat resin and the composite specimens. The response of each type of the sensor was studied and compared with the material parameters measured by additional independent experiments. The sensors have been found to be promising - yet, further development is required before they can be used in on-line monitoring of autoclave processing of polymer composites. Firsthand knowledge and experience on sensors, their installation, data acquisition, data processing, and data analysis have been generated through this study. Based on this knowledge, the advantages and limitations of sensors were evaluated and various issues that should be considered before using these sensors in real industrial environment were discussed. |
