Vibration Response Studies of a Bi-Morph SMA Hybrid Composite Using 3D Laser Doppler Vibrometer

With the advancement in the field of morphing and adaptive structures, there has been a tremendous increase in the application of such systems in the civil and aerospace engineering, especially wherever space constraint and variable operational environment demand frequent changes in system configuration. The control of stiffness and hence dynamic response of such deployable structures can be achieved through smart material based actuation mechanisms such as shape memory alloys (SMA), and piezoelectric active fiber composites. Selection of appropriate smart material hinges on the requirements of the speed of actuation, actuator bandwidth, and force requirement. In this work, we study the vibration modes of a bi-morph SMA reinforced composite with controlled current input. The composite consists of two layers of SMA reinforcements with 0° and 90° orientation angles placed orthogonally in alternate plies. The temperatures of these layers are raised through Joule heating, first individually, and then followed by combined actuation, where the current supply is controlled using a programmable DC supply. As the material properties of SMA are temperature dependent, we observe thermal contraction and a resulting increase in laminate stiffness. The change of compliance at multiple step-input current contributes to variation in the natural frequency which is recorded using a 3D laser doppler vibrometer (LDV). This study gives us a deep insight into the application of SMA-based bimorph composites for active damping and vibration control subject to varying temperatures.

Mathematical Modeling of an Active-Fiber Composite Energy Harvester with Interdigitated Electrodes

The use of active-fiber composites (AFC) instead of traditional ceramic piezoelectric materials is motivated by flexibility and relatively high actuation capacity. Nevertheless, their energy harvesting capabilities remain low. As a first step toward the enhancement of AFC’s performances, a mathematical model that accurately simulates the dynamic behavior of the AFC is proposed. In fact, most of the modeling approaches found in the literature for AFC are based on finite element methods. In this work, we use homogenization techniques to mathematically describe piezoelectric properties taking into consideration the composite structure of the AFC. We model the interdigitated electrodes as a series of capacitances and current sources linked in parallel; then we integrate these properties into the structural model of the AFC. The proposed model is incorporated into a vibration based energy harvesting system consisting of a cantilever beam on top of which an AFC patch is attached. Finally, analytical solutions of the dynamic behavior and the harvested voltage are proposed and validated with finite element simulations.

Characterization of Piezoelectric Nanofiber Composites Acoustic Emission Sensor for Structure Health Monitoring

A nanoscale active fiber composites (NAFCs) based acoustic emission (AE) sensor with high sensitivity is developed. The lead zirconate titanate (PZT) nanofibers, with the diameter of approximately 80 nm, were electrospun on a silicon substrate. Nanofibers were parallel aligned on the substrate under a controlled electric field. The interdigitated electrodes were deposited on the PZT nanofibers and packaged by spinning a thin soft polymer layer on the top of the sensor. The hysteresis loop shows a typical ferroelectric property of as-spun PZT nanofibers. The mathematical model of the voltage generation when the elastic waves were reaching the sensor was studied. The sensor was tested by mounting on a steel surface and the measured output voltage under the periodic impact of a grounded steel bar was over 35 mV. The small size of the developed PZT NAFCs AE sensor shows a promising application in monitoring the structures by integration into composites.