Characterization of a Fast Responding Composite Thermal Bimorph Film Actuator Based on Carbon Nanotube Sheets

Abstract

As the extraordinary thermal, electrical, and mechanical properties of carbon nanotubes (CNTs) have become better understood, they have found their way into a wide range of engineering applications. Used in conjunction with fiber-reinforced composite materials, CNTs provide enhanced thermal conductivity, interlaminar strength, and ballistic resistance of laminar composite materials. However, the direct application of the macro form of CNT sheet as a heating element for use in a thermal actuator has not been reported. In the present study, CNT sheets are used as a flexible, efficient, and fast-responding heating element that induces transverse motion in a multilayered functional polymer composite based on thermal expansion mismatch between layers. The CNT heating element is designed to have a specific cross-sectional area to length aspect ratio, giving it a specific resistance and power consumption characteristic. The heating element is bonded to a compliant silicone elastomer substrate and a stiff constraining polyimide thin film, forming a flap-like actuator. The robust design and simple operation of the actuator makes it a potential candidate for control surfaces on micro air vehicles and actuating elements in microscale fluid pumps. The heating response rate of the actuator is measured experimentally using an infrared thermal imager. The temperature change in the thermal actuator is measured as a function of input voltage. The edge deflection of the actuator is also measured as function of the applied voltage. Finally, finite element modeling of the thermal actuator, a parametric study of material selection, and deflection analysis are conducted to better understand the result of these experiments.