Piezo fiber composite

Piezo fiber composites Arrange andfill process... 

Figure 8. Left piezo fiber composite block material, right machined piezo fiber composite for transducer application...

Active fiber composites (AFC), macro fiber composites (MFC) [88,97] and piezo fiber composites (PFC) [87,98] are advanced variants of 1-3 composites that are particularly designed for adaptronic applications. Those variants are based on a basic design developed at the Massachusetts Institute of Technology (MIT) [89,93-96]. For that purpose uniaxial arranged piezoceramic fibers from PZT are embedded in a polymer matrix and contacted via interdigital electrodes at the surface. Such composites have a high flexibility and robustness and can therefore be easily applied to components or structures... 

Fig. 7.26. Schematic of the cross section of a 13 piezo fiber composite [88,89]...

For PVDF foil sensors and piezo fiber composites with 1-3 or 2-2 connectivity, the transversal sensitivity is very small and can be neglected under certain circumstances. 

Due to their high costs, weight and size conventional NDE ultrasonic transducers are not suited for active SHM applications. However, novel 1-3 composite transducers such as piezo fiber composites (PFC) are adapted quite well to SHM applications. They can be used for passive as well as for active methods i.e. as transmitters and receivers for ultrasonic waves. PECs are small, lightweight and extremely robust and thus can be structurally embedded for e-NDE purposes in a large number. 

The manufacturing of adaptive structures requires new production methods that need a lot of experience and expertise for the fabrication of complex systems with embedded or applied actuators and sensors. Patch-like sensors such as 1-3 piezo fiber composites are quite appropriate to be attached to the surface or to be integrated into lightweight multilayer constructions. The bond layer between the piezo element and the base structure determines the transfer behaviour of strain, vibrations and acoustic waves from the actuator to the structure and from the structure to the sensor. Local stress distributions can strongly be influenced by the bonding technique. 

Figure 16.9 Possible sensor configurations for composites SHM. (a) Local detection with piezo sensors [18] (b) local detection with optical fiber sensors [11] (c) sparse array of piezosensors guided-waves tomography for remote detection [19] (d) phased arrays of piezo sensors for remote guided-waves scanning.

When a unidirectional CFRP composite specimen is stretched, its longitudinal resistance decreases. This phenomenon (which may be due to both a transverse Poisson effect and carbon fiber piezo-resistivity) is reversible and the resistance returns to its initial value as the load is released. However, if damage occurs, irreversible resistance changes... 

Several methods have been used to determine the compression strength of carbon fiber and its composites—The Loop Test [90] Single Filament in a Beam [91] Critical Length under Compression [92] Micro-compression [93,94] Fiber Recoil [95-97] Piezo Method [98,99] Raman Spectroscopy [100-102] Composite [103,104] and Mini-composite [105]. 

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