OS17-2-2 Experimental characterization of Active Fiber Composites used as piezoelectric transducers for emitting and receiving Lamb waves in plate-like structures

Abstract

Active Fiber Composites (AFC) consist of one layer of piezoelectric ceramic fibers embedded in an epoxy matrix and sandwiched between two sets of interdigitated electrodes. They show orthotropic mechanical properties due to their design and manufacturing. The small thickness and the conformability to curved surfaces make them suitable for applications in structural health monitoring (SHM) with acoustic nondestructive testing methods. The piezoelectric properties of the AFC allow for both actuation and sensing capabilities with the same element which enables emitting and receiving of structural waves (e.g., Lamb waves) for monitoring of critical structural elements. Before realizing specific applications for AFC in SHM systems, it is necessary to characterize the transfer behavior of AFC bonded on a structure for excitation and sensing of transient waves which propagate in the structure. To characterize this behavior experimentally, the acoustic wave field in a thin, planar structure excited from surface bonded AFC is explored with a laser interferometer. Surface velocities at different positions around an AFC bonded on an aluminum plate during transient excitation are recorded. The transfer function is calculated for different angles from the fiber direction of the AFC for both the first symmetric and the first antisymmetric Lamb wave mode. The sensing process is also investigated: structural waves generated by surface bonded piezoelectric ceramic discs are measured likewise with laser interferometry in the vicinity of the AFC and with the AFC itself. Results show, that the emitting and receiving capabilities of the AFC decrease with increasing angle from the fiber direction of the AFC. Typical maxima and minima in the transfer function depend on the length of the AFC.