CeraNova
Corporation
Active Composites for Smart Structures
New: Transparent Ceramics
| Telephone: | 508 460-0300 |
| E-mail: | Info@CeraNova.com |
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| Telephone: | 508 460-0300 |
| E-mail: | Info@CeraNova.com |
|
Active PZT Fibers, a Commercial Production Process 2. ACTIVE FIBER COMPOSITES Active Fiber Composites (AFCs) originated from work started by Bent & Hagood1 (1992) sponsored by the Office of Naval Research. The concept is shown in Figure 2. Interdigitated electrodes (IDEs), with polarity aligned top-to-bottom and alternating in sign along each surface, are key to AFC performance. Interdigitated electrodes are used both for poling and to achieve electric field alignment along the longitudinally oriented and poled PZT fibers. In piezoceramics parlance, AFCs achieve greater actuation energy density by exploiting the d33 performance of fibers versus the d31 actuation of monolithic piezoceramic materials. AFC robustness and conformability are added advantages. The Consortium is targeting helicopter rotorblade aeroservoelastic control through twist actuation for eventual commercialization. Rodgers, Bent and Hagood2 (1996), have carried out the preliminary characterization work toward meeting the requirements of this high strain environment. Tests included electrical and mechanical fatigue, actuation level performance, stiffness and actuation degradation under high tensile loading, and others. The benefits of controlling the twist angle in helicopter blades has been evaluated through mathematical aerodynamic simulations by Derham and Hagood3 (1996). This evaluation of overall system performance, including economic merit, weight, and power consumption clearly justifies the use of AFC materials.
Figure
2: Active Fiber Composite design illustrating interdigitated electrode (IDE)
configuration. To maximize actuation authority and achieve practical electromechanical energy conversion density, the PZT fibers used in AFCs will have specific desired characteristics. For strength, important considerations are smooth fiber surfaces, uniform round cross sections, low porosity, and small grain sizes. For actuation capability, high performance points toward minimizing fiber diameter variations, and tradeoffs between electrodes and fiber diameter to achieve optimal levels of electric field in the fiber. A fiber diameter of ~130 micrometers appears to be a good compromise. Active fibers are embedded in a thermoset or thermoplastic polymer matrix. This provides structural integrity and a path for load transfer from surrounding composite plies to the active fibers. The polymer / fiber array is sandwiched between polyimide layers and an appropriate electrode structure. Recent work by Continuum is investigating a number of different electrode technologies with the potential of reducing sensitivity to manufacturing variability in high volume fabrication. Figure 3 illustrates one such electrode technology. Electrode conformability is thought to increase electric field penetration into the active fibers. The new electrode approaches show excellent electrical and mechanical fatigue resistance after 10 million repetition cycles. AFC cost will determine both military and commercial market acceptance. The CeraNova process will be integrated with AFC manufacturing concepts to minimize total manufacturing cost.
Figure 3: Cross section (a) and top view (b) of Continuum Control’s Active Fiber Composite using an experimental electrode system. Note conformability of electrode around fiber. Fiber diameter is 130 micrometers; electrode spacing is 1 mm with a width of 0.5 mm. |
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