Shape memory alloy (SMA) actuator consists of three subsystems: 1) SMA active element, 2) bias element to reset the system and 3) transmission. These three components have a direct impact on actuator capabilities. The main objective of this research project is to develop a design tool including the characteristics of its three subsystems. To do so, a systematic characterization methodology of SMA materials is developed to obtain its mechanical characteristics that define the actuation working envelope in the stress-strain space.
Firstly, a design methodology for a so-called "SMA passive bias actuator" is developed. This actuator type is defined by the combination of the SMA with a mechanical bias system as elastic spring. The design methodology is illustrated using CRIAQ 7.1 project (2006-2008) entitled "Laminar flow improvement of aeroelastic wing" in which the SMA actuators are used to modify the geometric profile of an airplane wing prototype. The actuator configuration consists of four subsystems: 1) SMA active element, 2) passive bias element (gas spring), 3) flexible extrados and 4) the transmission system. Fulfilling the requirements imposed by the morphing wing application to the force-displacement characteristics of the actuators, a novel design methodology to determine the geometry of the SMA active elements and their adequate assembly conditions is presented. This methodology uses the results of the constrained recovery testing of the selected SMA. Using a prototype of the morphing laminar wing powered by SMA actuators, the design approach proposed herein is experimentally validated.
Secondly, the influence of manufacturing parameters on the SMA properties is studied. The rolling mill is modified and a heating module placed before the deformation zone is developed. Thermo mechanical routes are defined by combinations of cold and warm rolling with intermediate annealing. These routes are compared to determine the processing conditions that will best allow the production of nanostructured Ti-Ni shape memory alloy, while reducing mechanical damage from rolling and enhancing the material texture. The processed alloy is characterized using constrained stress recovery technique in cyclic regime. The results of such a comparative functional characterization of nanostructured Ti-Ni alloy obtained by six different manufacturing routes are discussed. The warm rolling decreases the stress recovery and leads to longer fatigue life due to a higher ductility and lower damage accumulation during deformation.
It becomes important to develop a simple, fast and effective methodology for characterizing SMA actuator to obtain quickly the capabilities of the active element (working envelope). To address this problem, an automated test bench dedicated to the systematic SMA characterization has been developed. This test bench has several objectives: 1) to characterize the SMA active element (force and stroke generated), 2) to simulate the behavior of passive bias actuators and 3) to simulate the behavior of active bias actuator. A multitude of strainstress characteristics can be replicated to mimic real application conditions. Therefore, the developed test bench could support both the design and validation phases of an SMA actuation system development process.
Finally, the development of the automated test bench allows the study of active bias SMA actuators where two active elements are connected together. The objective with this type of SMA actuator is to reduce the system weight and increase the actuation capabilities by an independent temperature control of each SMA. This part focuses on the development of a systematic experimental approach for performance evaluation of active bias SMA actuators. A specific combination of different characterization modes applied to these actuators is used to evaluate the work generation potential of active bias SMA actuator in multiple-cycle actuation mode. An application example is presented to illustrate and understand the characterization methodology of this type of SMA actuator.
Georges, T. (Author),
Brailovski (Supervisor) &
Terriault (Co-supervisor),
4 Jan 2012Student thesis: Doctoral thesis › Doctorate in Engineering: Engineering