TITLE: Combined Sensor System for Cure and In-Service Health Monitoring of Composite Structures

Abstract:
Advanced composite materials have evolved into the class of materials which meet the strict requirements of many ground and space-based critical structures. Structures which incorporate these novel materials are frequently exposed to harsh environments during service, and must therefore be manufactured using high quality standards. Not only is it desirable to monitor and control the fabrication process using embedded sensors, but it is also necessary to instrument these structures with devices which allow in-service health monitoring.

This paper describes an approach which integrates a fiber optic (FO) cure monitoring sensor with optical time domain strain sensors for cure and in-service health monitoring of composite structures. The cure monitoring sensor consists of a sensing fiber manufactured from a thermoset composite resin itself (resin sensor). The strain monitoring sensors consist of optical fibers which are segmented with partially reflective markers distributed along the length of the optical fibers. The cure state of the composite resin can be determined insitu during the fabrication process by monitoring the intensity and the time delay of the optical signal through the resin sensor waveguide. By monitoring the cure state of the composite resin, decisions can be made in real-time to constantly modify and optimize the cure cycle. Strains can be measured by monitoring the time delay of the optical signal through the strain sensor waveguides to detect local strain changes caused by temperature, pressure, or process induced residual stresses. After cure, the strain sensors can also be used to monitor structural integrity during service applications. Experiments conducted using press cure to evaluate resin sensor performance and subsequent mechanical testing to evaluate strain sensor performance will be discussed.

Source: Proceedings of the 'NDE applied to Process Control of Composite Fabrication' - Conference, 4-5 Oct 1994 St. Louis, Missouri. Publisher and Organizer: Nondestructive Testing Information Analysis Center (NTIAC) Texas Research Institute Austin, Inc. Austin, Texas [http://www.ntiac.com] [Buying the Proceedings]