Recently, the focus of application for advanced composite materials has turned from aerospace to civil, mechanical and transportation industries. The properties of a composite structure can be tailored during fabrication to meet the design criteria of its application [1]. While composites have traditionally found application in aerospace, sporting goods, and marine fields; they have recently been used in civil engineering structures, including monitoring, rehabilitation projects, prestressing tendons, reinforcing bars, and most recently as innovative structural members of bridges [2]. For these reasons, composite materials lend themselves as prime candidates for another rapidly expanding field of research known as "smart materials". A smart material is a structure which contains a built in sensing device to continuously monitor the current state and serviceability of the structure. This is referred to as a "passive" smart material which has many applications in civil engineering. More sophisticated smart structures have embedded sensors to monitor performance; the ability to compare the measured data to specification; and the means to apply corrective forces through embedded actuators. These structures are called "active" smart materials (or intelligent materials) and have the most potential for application in high precision engineering structures. Composite materials are good candidates as smart materials because their "build up" fabrication techniques inherently allow for the embeddement of sensors and communication lines. Current inspection techniques utilized in the aircraft industry require a structure to be taken out of service, which can be a time consuming and expensive process. The proposed smart structure will yield continuous and real time measurement of critical parameters, and feed this information to an aircraft pilot, or perhaps technicians assigned to monitor the performance of a number of bridges.
The initial sensing of a smart composite material can be achieved with optical fibers which can act as both sensor and data transmitter. There are a variety of fiber optic sensors which can measure such external forces as pressure, temperature, strain, and vibration. A key advantage with embedded optical fibers is that their small size does not greatly effect the mechanical properties of the composite reinforcement.
The issues to be addressed in the present study include:
- the manufacturing technology for the smart composite reinforcements, from hand layup fabrication to more automated processes such as pultrusion, filament winding, or tape laying;
- the choice of appropriate fiber optic sensors;
- interconnection of components;
- application for the non-destructive testing and monitoring of structures; and
- comparison with the traditional testing techniques.
Acknowledgment
This work has been supported by the ISIS-CANADA NCE (The Intelligent Sensing in Innovative Structures Canadian Network of Centres of Excellence) through the Project T3.4 on Smart Reinforcements and Connectors. REFERENCES
- A. L. Kalamkarov, "Composite and Reinforced Elements of Construction", Chichester, New York: John Wiley & Sons, 1992
- A. T. Alavie, R. Maaskant, M. M Ohn, S. Rizkalla and R. M. Measures, "Application and Characterization of Intracore Grating Sensors in a CFRP Prestressed Concrete Girder", Proc. "Smart Materials and Structures", SPIE-Vol. 2191, Orlando, February 1994.
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