Characterization and modeling of active fiber composites

Open Access
Author:
Ben Atitallah, Hassene
Graduate Program:
Mechanical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 12, 2014
Committee Members:
  • Zoubeida Ounaies, Dissertation Advisor
  • Zoubeida Ounaies, Committee Chair
  • Clive A Randall, Committee Member
  • Mary I Frecker, Committee Member
  • Charles E Bakis, Committee Member
Keywords:
  • Piezoelectricity
  • composites
  • Temperature dependence
  • AFC
  • Viscoelasticity
Abstract:
Active Fiber Composites (AFCs) are long fiber composites, where the fibers are made from lead zirconate titanate (PZT), which is one of the most widely used piezoelectric materials owing to its high electro-mechanical coupling and high piezoelectric coefficients. The PZT fibers are embedded in an epoxy matrix to give the composite more flexibility and more ruggedness. AFC utilizes interdigitated electrodes (IDE) along the direction of the fibers resulting in a d33-mode actuation (actuation parallel to the poling direction), which is advantageous since the d33 coefficient is almost twice the value of the d31 coefficient (actuation perpendicular to the poling direction). The development of AFCs offers a great potential for advancing structural health monitoring techniques and active vibration control and suppression thanks to their flexibility and lightweight, however AFCs piezoelectric performance is still not comparable to that of PZT transducers, where their effective actuation coefficient is 120 compared to 400x10-12 m/V for the bulk PZT. In addition, while in use, AFCs could be subjected to simultaneous mechanical loading, extreme environments, and moderate to high electric fields, leading to nonlinear and inelastic behaviors, strong coupling between various physical properties, and complex failure mechanisms. Moreover, AFCs have more than 50% volume content of polymer; the viscoelastic effect of the polymer matrix on the overall response of AFC can be significant especially at elevated temperatures. The effects of time and temperature on the mechanical and electrical characterization of AFCs have not been studied. Modeling these phenomena for the AFCs is an important step in redesigning them and obtaining reliable properties. However, there is not an available model that takes into consideration combined physical phenomena like time-dependence and piezoelectric non-linearity. In addition many models assume uniform electric field or perfect contact between the fibers and the electrodes, which neglects the effects of any IDE geometry parameters and electrical property of the matrix. The overall objective of this proposed dissertation is to use a combination of experimental and numerical approaches to examine the overall behavior of the AFC with the goals of 1) quantifying the impact of the constituent properties (polymer matrix and PZT fiber) on coupled response of AFCs, 2) conducting an exhaustive parametric study focused on design of AFCs, and 3) building a model which takes into consideration non-uniform electric field behavior, non-linear behavior and time-dependent properties. Mechanical, electrical and electro-mechanical experimental characterization of AFC and its constituents at various temperatures and loading rates were carried out to bring to light the behavior of AFC, including the time and temperature dependence of some of its properties. Numerical parametric study on the design of the composites that takes into effect the IDE geometry and matrix dielectric constant and modulus is conducted. In addition, the experimental work quantified the non-linear and time-dependent responses of the AFCs, which are then included in the developed model. One outcome of this study is to propose a re-design of an improved AFC device with better electro-mechanical coupling response.