Thermaly Active Structures for Shape Morphing Applications

For shape morphing application, thermal activation coupling to a bimetallic strip effect can be a substitute for classical actuators, piezoelectrical or shape memory alloys. The controlled behaviour of composite material (CBCM) is a thermaly activated composite material. The thermal activation is made thanks to carbon yarns which are connected to a power supply. If the anisotropy of the structure is well organized, the desired deformation is reached when the temperature within the composite is rising. To obtain a CBCM morphing composite structure, it is necessary to design a specific structure. The aim of this work is to show that it is possible to adapt the CBCM principle in order to transform any kind of classical composite structure to an active structure. The first part of this work consists in presenting the experimental results for two examples of composite beams. The second part is about the active structure FEM modeling and the development of adapted tools for this particular design. 1. Introduction Because of their capacity of actuation, morphing structures are used to simplify mechanisms by reducing the number of moving parts. Three main actuation technologies are commonly used: piezoelectricity, shape memory alloys, or thermal effect. In the case of a structure with bistable effect, these technologies are used to activate the shape changing by piezoactuation [1–3], SMA actuation [4–6], and thermal actuation [7–9]. The field of applications for bistable structures is limited because they have only two positions of stability witch are not adjustable and link to the structure geometry. In the case of standard not bistable composite structures, the main problem is the link between the composite and the actuator. Many works can be found with SMA [10, 11] actuators or piezoactuators like macro-fiber composite (MFC) [12, 13], but the interface strength between the actuator and the composite plays a crucial role in the time life of the structure that is a limit especially when the rigidity of the composite structure is high. To overcome problems of bonding between the actuator and the structure, the bimetallic strip effect coupled to an internal thermal actuation can be a solution. Indeed the whole structure can be considered as an actuator, and the problems of interface decohesion are not concentrated at the interface actuator/structure but distributed all along the interfaces of the laminate composite. Controlled behaviour composite material (CBCM) [14–18] is a thermal actuator developed ten years ago. There are two different ways to use the CBCM