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. This actuator structure can be bent by heating, even though it is lightweight and has a moderate bending stiffness. First, unidirectional CFRP skins were bonded to the SMA honeycomb core made of thin SMA foils and a pre-shear-strain was applied to the SMA core. Then the ends of the upper and lower skins were fixed together to other cores. The length of the sandwich beam specimen was 18cm, and the weight was only 9.2g. When the specimen was heated, the beam was bent upward taking the form of a sigmoid curve and generated the sufficient actuation force. Then, when the specimen was cooled to the room temperature, the beam returned to the initial straight shape. Hence the two-way actuation is possible. This method has the better ability to bend skins with high in-plane stiffness, because the recovery shear force has the out-of-plane stress component and is applied uniformly to the skins from the inner core. Also the microscopic mechanism of this bending deformation could be clarified by a numerical simulation with the finite element method. Furthermore, this actuator structure has a possibility to be used as a member to suppress the resonance, because the natural frequency of the beam can be controlled owing to the increase in the elastic moduli of SMA by heating.