Lightweight Actuator Structure With SMA Honeycomb Core and CFRP Skins

The authors proposed a sandwich structure that consists of a shape memory alloy (SMA) honeycomb core and carbon fiber reinforced plastic (CFRP) skins as a shape-controllable structure. The proposed lightweight actuator structure can be bent by heating even though it has a moderate bending stiffness. First, unidirectional CFRP skins were bonded to the SMA honeycomb core made of thin SMA foils, and residual shear strain was applied to the SMA core. Then, the ends of the upper and lower skins were fixed to other cores. The length, thickness, and width of the sandwich beam specimen were 180 mm, 16 mm, and 13 mm, respectively, and its weight was 9.6 g. Hence, the effective density of the entire beam was only $0.26g/cm3$⁠. When the specimen was heated, the beam either bent upward, taking the form of a sigmoid curve, or generated a moderate blocking force. When the specimen was cooled to room temperature, the beam regained its initial straight shape. Therefore, a two-way actuation is possible. This method has a better ability to bend skins with high in-plane stiffness because the recovery shear force has an out-of-plane stress component and is applied uniformly to all the skins from the inner core. In addition, the microscopic mechanism of this bending deformation can be clarified by a numerical simulation with a finite element method. Furthermore, the proposed actuator structure can possibly be used as a member that suppresses resonance since the natural frequency of the beam can be controlled by increasing the elastic moduli of SMA on heating.