Shape memory alloys (SMA) provide common solid state actuators with reliable and unique characteristics. Their special behavior is based on a reversible phase transformation and can provide high power density, induced strain and block force which render them indispensable for use in morphing structures that require large shape changes while space and weight restrictions are imposed. Yet, their implementation into morphing structures faces challenges related to their complex multi-disciplinary behavior, their interaction with the passive structural components, geometrical nonlinearity due to large shape changes, the lack of experimental data, and above all, the lack of modelling tools which can robustly simulate the complex thermomechanical behavior and make feasible their design. We briefly review the material characterization process, the developed modelling tools which can simulate the complex thermomechanical response of morphing structures with SMA actuators which can undergo large shape changes under severe geometric nonlinearity, and the testing of prototype morphing components. The design and validation of two morphing structural concepts for curvature control are presented. A morphing strip capable to deform towards a single target shape is initially presented. Subsequently, a morphing airfoil concept implementing an articulated mechanism capable to achieve multiple target shapes for aerodynamic load control is presented. The challenging task to continuously adapt the structural shape to time varying demands, dictates the use of antagonistic actuator configurations to maximize and control the range of morphing. The previously mentioned morphing airfoil configuration is used to alleviate the aerodynamic fatigue loads in wind turbine blades and aircraft wings.
Design of Structures That Adapt to Loads through Large Shape Changes
