Active Fibre Composites

From our earlier discussion in lecture 30, it may be noticed that the magnitude of piezoelectric constant d₃₃ is significantly higher than d₃₁ . For example, for a soft piezoelectric material d₃₁ is about -55 pC/N, whereas d₃₃ is around 190 pC/N. Similarly, for a hard piezoelectric material, d₃₃ is 2.5 times higher than d₃₁.

Internally leveraged piezoelectric actuators like piezo-stacks are developed exploiting this property. This has also encouraged the material scientists to develop piezoelectric fibres and actuate them axially to generate larger actuation strain. Later, these fibres are embedded inside a polymeric matrix to form composite actuator and sensor.

Two types of smart composites have been developed using piezo-ceramic fibres;

Active Fibre Composite (AFC)

Macro Fibre Composite (MFC)

The difference between AFC and MFC is in the manufacturing process of the fibre. While the AFC fibres are developed using standard sol-gel technique, the MFC fibres are essentially chopped from PZT blocks. The MFC fibres are rectangular in cross-section and hence it offers better electrical contact between the fibres.

Such fibres are proposed to be used for the following applications:

• actuators and sensors
• structural health monitoring
• active/passive vibration damping