Development of an active structural fiber for multifunctional composites

Multifunctional materials are defined as structural materials which carry external mechanical loading as well as exhibit at least one additional performance related function. One potential candidate for use as a multifunctional constituent is piezoceramic material, which exhibits the unique capability of coupling the energy between mechanical and electrical domains. Piezoceramic fiber composites have been developed by embedding piezoceramic fiber into a flexible polymer matrix which protects the fiber from breakage under mechanical loading. However, due to their poor mechanical strength and surface bonded interdigitated electrodes, previously developed piezoelectric fiber composites can not be embedded into the material system and provide little strength increase to the material system.;The testing results were consistent with those predicted by the models, which validated the accuracy of the models and indicated that the effective longitudinal electromechanical coupling could reach as high as 70% of that of the bulk active constituent used. Energy storage capability of this active structural fiber was also characterized and the results determined that the energy density of this multifunctional design was two orders of magnitude higher than those structural capacitors in literatures. Finally, the interfacial shear properties of this multifunctional composites design were explored through a single fiber pullout test. This simplified design enables the electromechanical functionalities typically performed by piezoelectrics such as structural health monitoring, dynamic sensing and actuation, energy storage and vibration damping and control to be directly embedded into the load bearing medium, which has not been possible with existing piezoceramic fiber composites.;In order to alleviate issues associated with current piezoceramic fiber composites; this dissertation introduces a novel active structural fiber for multifunctional composites. The active structural fiber was developed by coating a silicone carbide fiber with a piezoceramic layer, where the core fiber serves as the inner electrode for the piezoceramic shell and carries external mechanical loading. A three dimensional micromechanics model was developed to predict the full effective electroelastic moduli of the multifunctional composites with different design parameters. Effective electromechanical coupling of both the active structural fiber and single fiber lamina were characterized by an atomic force microscope using an inverse piezoelectric effect.