As the aerospace sector aims to decrease its greenhouse gas emissions from historical levels, vehicle lightweighting is seen as key to achieving meaningful reductions in the sector. Shape memory alloy (SMA) materials have been shown to have extremely high work density that, when applied in an actuator, can yield significant weight savings compared to electric motor and hydraulic powered alternatives.

Shape memory alloys (SMA) provide a compact, robust, light-weight and scalable rotary actuation technology suitable for many aerospace applications that require precise control and high torque. Over the last 25 years Boeing has fabricated, processed and characterized several hundred NiTi-based tubes with the objective of optimizing performance for aerospace applications. The effects of supplier, material composition, processing, heat treatment, training parameters and component size were characterized and mapped in NiTi and NiTiHf systems. The effects of lower and upper cycle temperature (LCT and UCT, respectively), applied torsional loading (including nominal, minimum, maximum, reversed and varying), rotational limits (blocking) and repeated thermal cycling (to over 100,000 cycles) were systematically investigated. Based on those results, torsional SMA components were fabricated for optimal performance and evaluated under repeated thermal cycling under load to assess their ability to meet actuator requirements for an applications’ required life cycle. Additionally, isothermal torque-deflection and constant torque thermal cycling test (similar to E3414) have been performed across all relevant actuator parameters. This paper reviews and summarizes test outcomes, providing additional insight into the design and characterization of SMA rotary actuator components in context of the SMA material, component processing, operational parameters and their intended use in applications.

Shape memory alloys (SMA) provide a compact, robust, light-weight and scalable rotary actuation technology suitable for many aerospace applications that require precise control and high torque over a discrete output range. With their compact form factor and high energy density, SMA rotary actuators can often be directly integrated into or near a hinge line reducing the need for complex kinematics (e.g., linkages and gears) that are typically required to transfer the work from a rotary actuator’s output to an effector such as a flap or aileron. Boeing has executed high technology readiness level (TRL) demonstrations and production use of scalable SMA rotary actuation technology across several size scales and aeronautical platforms. Applications range from wind tunnel models to full-scale laboratory demonstrators and flight tests. Successful demonstrations include reconfigurable vortex generators, actuated wind tunnel models, adaptive trailing edges, power door opening systems, spanwise adaptive wings, variable area nozzles and variable geometry structures.

NiTi shape memory alloy (SMA) actuators have gained much attention in recent years because of their ability to combine high actuation forces to a significantly smaller component size. Binary SMAs containing Ni and Ti, however, suffer from relatively poor functional and structural fatigue, which requires training. Binary NiTi SMAs also possess a relatively wide hysteresis gap between the austenite final and martensite final temperatures (ΔT MfAf ), which demands more energy to produce each actuation stroke. Zarnetta et al. have shown that small additions of substitutional elements to the NiTi-based SMA can significantly improve those conditions by increasing the coherency between the two transforming crystal structures. Two quaternary NiTiCuPd SMAs were selected based on combinatorial studies from X-ray diffraction data and their results were analyzed concerning their hysteresis width and thermal-mechanical stability.

Conventional vortex generators (VG) in aeronautical applications are static vanes mounted on aircraft surfaces used to improve aircraft efficiency during low speed operations. However, during the cruise phase of flight, these static devices are always deployed and produce drag penalties. With the goal of improving aircraft efficiency, Boeing in collaboration with NASA Glen Research Center have developed and successfully flight tested environmentally activated SMART-VGs that repeatedly and accurately retract during cruise and deploy during take- off and landing. This application is distinctively enabled by the ability of shape memory alloy (SMA) actuation to produce large work outputs in compact volumes and operate as both a sensor and actuator. The SMART-VG project highlighted here was built upon recent advancements in SMA rotary actuation technology that included improved alloy systems, design tools, best practices, published standards and high-level wind tunnel and flight test demonstrations. This program successfully matured and validated the targeted alloy development and associated design processes in a unique way by demonstrating shape memory alloy reconfigurable technology (SMART) in-flight. The data from this flight test is being used to optimize a next generation design of the SMART-VGs that will be tested in 2022.

Shape memory alloys (SMAs) have gained attention in recent years as a powerful mechanism for mechanical actuation in space applications. One issue facing this technology is that most commercially available SMAs yield a high amount of energy loss due to their relatively large hysteresis, which can translate into an increase in the overall cost of the mission. Low hysteresis shape memory alloys (LHSMAs), which exhibit a much narrower hysteresis, are needed to minimize this energy loss. Previous studies have shown that elemental additions of Cu, Co, and Pd to the NiTi-based SMA can result in shape memory alloys with a much lower thermal hysteresis, due to better phase compatibility. This present work investigated seven alloy compositions to identify LHSMAs with less than 20 °C hysteresis and develop processing routes for these LHSMAs to determine potential candidates for space actuation applications.