R-phase actuated SMA composites in adaptive wind turbine blade trailing edge

There is an interest of doubling or quadrupling the rated power of wind turbines from the present maximum of about 5 MW, especially for offshore applications. This increases the blade length to about 80 or 100 m. The growth in size of blades is not feasible using the present technologies and materials. Also the slenderness of wind turbines leads to increased importance of vibration and fatigue control of blades and supporting structures. These increasing requirements call for new structural concepts and advanced materials and also for more adaptive solutions. Better control of the turbine such as advanced blade pitch control or shape control or their combination has to be developed and utilized. The one key issue is reduction of the fatigue loads of blades and that way increasing the life of the structure and enabling use of the turbine at higher wind speeds and gusty winds, which would increase the power production. Shape memory alloy (SMA) composites as morphing structures have been studied widely. In this study possibilities of SMA composites based on utilization of pre-martensitic R-phase transformation were determined. Special treatments to achieve pure R-phase transformation were developed and thermo-mechanical properties of the wires were determined. R-phase actuation has been found to offer several beneficial features compared traditional austenitemartensite transformation. The studies revealed that hysteresis can be remarkably decreased, leading to higher operating frequency at lower temperatures. One of the most important features of R-phase actuated wires is their superior resistance against functional fatigue compared to traditional SMA wires. A novel manufacturing route for SMA composites was developed. Laminate and actuator test structures were designed by FE modeling. R-phase actuated SMA composites were demonstrated at wind turbine blade adaptive trailing edge. In laboratory condition 5° change in camber of trailing edge was achieved when wires were heated up 60 °C. Effect of wind speed on the achieved shape changes was studied by preliminary wind tunnel tests.