Processing monitoring of carbon/phenolic composites using smart sensors

Abstract

High void content and delaminations are observed during the fabrication of thick carbon/phenolic composites due to the high percentage of volatile release which occurs during polymerization. In order to eliminate these imperfections and enhance product quality for thick carbon/phenolic composites, smart sensors are used to monitor the property changes during the processing and control of the component to minimize this effect. This paper describes a technique to monitor and collect sensor data during the curing process of a general material system. Data obtained from sensors are used to generate an expert processing knowledge base which automatically controls the composite cure state based on direct sensor response, in lieu of classical time/temperature techniques. Microdielectric, ultrasonic, thermopile, thermal couple and extrinsic Fabry-Perot interferometer (EFPI) sensors are investigated as potential candidates to monitor and subsequently control the manufacturing process of a composite material. Microdielectric sensors are used to monitor resin property changes. Ultrasonic sensors are used to measure stiffness changes and porosity development in the composite material. Thermopile and thermal couples are used to monitor temperature variance and heat reaction rates within the material. EFPI sensors, historically used for monitoring structural integrity during service applications, are used to detect local strain changes caused by temperature, pressure, or process induced residual stresses. In addition to classical optical sensors, a modified EFPI thermal sensor is employed to monitor temperature variations.