Active fiber composites for structural health monitoring

An embedded active fiber composite tape was investigated for use as a sensor for structural health monitoring. The material has unidirectional piezoceramic fibers with interdigital electrodes on the top and bottom surfaces and is poled in the fiber direction. A long active fiber composite tape with segmented electrodes was modeled as a sensor to measure longitudinal stress waves in a uniform cantilever bar. Only plane longitudinal standing and traveling waves in the bar are modeled. The sensor was connected to an electrical tuning circuit to filter out undesirable noise due to ambient vibrations. The elastic response of the bar was computed in closed form at small time steps, and the coupled piezoceramic constitutive equations and the electrical circuit equations were solved by numerical integration using the Newmark-Beta method. Strain vibration and wave propagation responses were computed in the simulations. The simulations indicate that such a sensor will be capable of detecting damage to the bar from the changes in the wave propagation response. Further, the sensor has adequate sensitivity to detect fiber breaks in the composite bar. An active fiber composite patch was also tested to measure vibration and simulated acoustic emissions.