Long term reliabilty of active fiber composites (AFC)
A dissertation submitted to the
Swiss federal institute of technology
Zurich
for the degree of
Doctor of Sciences ETH Zurich
presented by
Mark Melnykowycz
Abstract
AFC are composed of piezoelectric Lead Zirconate Titanate (PZT) fibers encased in an epoxy matrix. The combined mechanical and electrical properties of PZT make AFC ideal as sensor and actuation devices, which can be integrated into composite laminates. This enables the manufacture of structural composite laminates with active properties.
Although already studied as an actuation system, the sensor function and reliability of AFC has not been investigated. Furthermore, the fiber failure and fragmentation behavior has not been fully studied, and methods for improving the structural properties of AFC have not been proposed.
The current work uses mechanical characterization techniques to characterize AFC strain sensor behavior including fragmentation in the PZT fibers, the influence of electrode placement on fiber failure and how AFC integration affects the integrity of glass and carbon fiber laminates is also presented. While AFC integration affected composite laminate integrity, this impact could be mitigated by integrating AFC into cross-ply as opposed to woven laminates.
Active laminates with AFC were shown to exhibit excellent fatigue reliability so long as the integrity of the PZT fibers was not compromised. Fiber cracking occurs near electrode edges due to the modification of fiber material properties resulting from electrical polarization of the fibers. The use of a pre-stressed CFRP interface was used to effectively place PZT fibers in compression and thereby extend the strain region of the AFC.
