Abstract The CASMART Processing Working Group presents a comprehensive review of processing routes for NiTi-based shape memory alloy (SMA) and high-temperature SMA (HTSMA) torque tubes, covering techniques ranging from extrusion, drawing, and gun-drilling to electrical discharge machining, laser cutting, combustion synthesis, and multiple additive manufacturing approaches. Structured case studies addressing raw materials, process flow, characterization, post-processing treatments, and thermomechanical performance of each route.

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. Following a collaboration between Kinitics Automation Limited (Kinitics) and The Boeing Company (Boeing), a high torque rotary actuator was developed which can be scaled to accommodate a wide range of aerospace applications. Developed as a line replaceable unit (LRU), the rotary actuator needed to meet strict requirements as are typically demanded by the aerospace sector. By leveraging the reconfigurable nature of the actuator, two SMA tube elements were tested under various loads. Conversion of applied torque and angular displacement into the SMA tube elements shear stress-shear strain behavior allowed the elements to be directly compared. Analysis of the data indicated significant differences in the actuation shear strain capabilities of the two SMA elements under test. Benefits of utilizing the actuator as an in situ SMA element tester included reuse, interface simplification, and reduced uncertainty.

Abstract 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 (ΔTMfAf), 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.

Abstract 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.

Abstract 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.

Remote Control Actuation (RCA) of wind tunnel models provides a paradigm shift in wind tunnel testing. Traditional wind tunnel testing involves fabricating and testing numerous fixed parts requiring time consuming model changes in order to test configurations of interest. RCA wind tunnel models seek to replace these fixed wind tunnel parts with moving, controllable parts. Thus RCA enables increased productivity, improved data quality, and reduced cost of wind tunnel testing. An international team from Boeing, Deharde Maschinenbau, European Transonic Windtunnel (ETW), and NASA Langley Research Center has developed and tested multiple RCA models in high speed cryogenic wind tunnels in order to demonstrate, scope, and validate the technology. Over the last decade, multiple RCA enabled wind tunnel models were designed, built, and tested at cryogenic high speed tunnels such as NASA Langley and ETW enabling the technology to mature with each iteration, Figure 1. Tests of multiple models are described here along with design and testing best practices. A 2D airfoil with a controllable spoiler provided an efficient platform to develop and demonstrate RCA capabilities. The spoiler system included an integrated solid-state actuator using Shape Memory Alloy (SMA), mechanisms for torque transmission and braking, integrated sensors and electronics, and advanced controls. The spoiler airfoil was designed to incorporate a suite of sensors, including pressure taps, thermocouples, spoiler position sensors, and strain gages for load sensing. The team designed, built, assembled, and laboratory tested the 2D spoiler test article prior to operational testing in Pilot European Transonic Windtunnel (PETW) and NASA Langley Research Center 0.3-Meter Transonic Cryogenic Tunnel (TCT). Later improvements to the model were made to increase rate and precision. Modifications included highly robust, next generation Nickel-Titanium-Hafnium SMA actuation elements, efficient induction heating, and an improved control system. The system was tested at NASA TCT in 2021 demonstrating a 10x rate improvement, more precise spoiler angle control down to 0.1 degrees, and robust disturbance rejection. The system performance was remarkably stable over the five day test period and provided a performance expectation for future wind tunnel models. The RCA technology was validated for cryogenic high-speed wind tunnel testing during production-type testing of a modified 4.5% 787-8 half-model with multiple RCA surfaces at ETW main tunnel. Three primary RCA surfaces: aileron, outboard spoiler (OB Spoiler) and inboard spoiler (IB spoiler) were designed, built and tested based on lessons learned and best practices from previous tests over the preceding 4+ years, in particular the initial testing of the 2D inboard Spoiler. The test demonstrated a 90% reduction in wind tunnel test time using RCA surface rather than changing out traditional fixed parts. The test identified challenges for RCA wind tunnel testing, including the ability to hold position under rapidly changing loads. Subsequent development and testing of the 2D Spoiler model demonstrated technical solutions to these challenges. The improved 787 model will be tested at the NASA Langley National Transonic Facility (NTF) in early 2023. RCA wind tunnel testing has matured over multiple design, build, test iterations resulting in a commercial ready technology that is fundamentally changing wind tunnel testing. This presentation describes the design and testing of these wind tunnel models and provides a glimpse at the future of the technology that will provide significant benefits to aerospace vehicle development.

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.

Design and development of innovative material compositions and mechanisms based on shape memory alloys (SMAs) were accomplished as part of the Consortium for the Advancement of Shape Memory Alloy Research and Technology (CASMART) 2nd student design challenge. The challenge consisted of developing an expandable space habitat where the retention and deployment of such structure employs the use of SMAs. Student groups were provided with an initial set of requirements and given an option to design the material or design with the material, within six months. This paper collectively documents the evaluation, alloy selection, fabrication, testing, and implementation processes of three teams, including the tools and information used to successfully design, develop, and implement SMA material systems and habitat technologies. For the mechanism design, students used a combination of superelastic rods and shape memory springs/wires to design collapsible rings to fold and deploy the habitat. Publicly available design tools were used to size the SMA components based on the provided loading scenarios. For the material system development, compositions based on CuAlMn, NiTiFe, NiTi and NiTiSn alloys were explored and designed to satisfy the given set of requirements. Details pertinent to these designs are described in this work, along with lessons learned.

Thermoelastic deformation mechanisms in polycrystalline biomedical-grade superelastic NiTi are spatially mapped using in situ neutron diffraction during multiaxial loading and heating. The trigonal R-phase is formed from the cubic phase during cooling to room temperature and subsequently deforms in compression, tension, and torsion. The resulting R-phase variant microstructure from the variant reorientation and detwinning processes are equivalent for the corresponding strain in tension and compression, and the variant microstructure is reversible by isothermal loading. The R-phase variant microstructure is consistent between uniaxial and torsional loading when the principal stress directions of the stress state are considered (for the crystallographic directions observed here). The variant microstructure evolution is tracked and the similarity in general behavior between uniaxial and torsional loading, in spite of the implicit heterogeneous stress state associated with torsional loading, pointed to the ability of the reversible thermoelastic transformation in NiTi to accommodate stress and strain mismatch with deformation. This ability of the R-phase, despite its limited variants, to accommodate stress and strain and satisfy strain incompatibility in addition to the existing internal stresses has significance for reducing irrecoverable deformation mechanisms during loading and cycling through the phase transformation.

Shorter engine inlets and more compact nacelles are being considered to reduce weight and drag of future commercial airplanes. Such designs may have significantly less area for acoustic treatment. Coupled with engine designs with lower blade passage frequencies and anticipated further stringency for airplane noise certification, the need arises for acoustic liner designs capable of a broad range of attenuation frequencies. With this in mind, a collaboration between Boeing, NASA and Florida State University was formed to develop active acoustic liner technologies to optimize acoustic performance and reduce drag during various stages of flight. One such concept is an active acoustic liner facesheet utilizing shape memory alloy (SMA) technology. A three layer facesheet with an actuated middle layer allows for the facesheet perforation to be sealed when noise attenuation is not required, thereby potentially reducing inlet and aft fan surface drag. This concept also allows for acoustic liner optimization in flight through altering the middle facesheet layer position, allowing for different size perforations to be achieved. This type of acoustic design has been explored in the past for the beneficial acoustic characteristics described above. However, up to this point, there have been limited efforts to develop methods to actuate, manufacture and integrate these designs in practice. This paper highlights the design, fabrication, test, and resulting analysis of the SMA facesheet development process. It will also discuss the successes, challenges, and potential future of active acoustic liner technology. Finally, preliminary impedance data will be shown that illustrates a potential design space for this active liner system.

Traditional wind tunnel testing dictates the fabrication and testing of numerous fixed parts requiring time consuming model changes to test multiple configurations of interest. Remotely actuated components using hydraulic or electric actuators are commonly used in many wind tunnel model designs to increase productivity; however, they have not been shown to be a viable solution for cryogenic wind tunnel testing. Utilizing remotely controlled actuation (RCA) of shape memory alloy (SMA) based actuators has shown to be a viable solution to replace fixed wind tunnel parts with instrumented components able to controllably, accurately and repeatably move to a fixed position under all conditions experienced within a typical high-speed or high-lift test campaign, without tunnel access, thus enabling a significant increase in productivity, improved data quality, and reduced cost of wind tunnel testing while acquiring flight Re data early in the development cycle. An international team from Boeing, Deharde, the European Transonic Windtunnel, and NASA developed and repeatedly tested two 2D RCA airfoils between 2014 and 2018 with controllable surfaces to demonstrate and assess the maturity of this technology. The airfoils incorporated a suite of sensors, including pressure taps, thermocouples, control surface position sensors, and strain gages for load sensing. Next steps include integration and test of multiple RCA elements within a 4.5% 787 semi-span production model. RCA spoiler test article design, testing, and resulting analysis is presented along with the successes, challenges, maturity levels and future of this innovative technology.

The primary goal of the Consortium for the Advancement of Shape Memory Alloy Research and Technology (CASMART) is to enable the design of revolutionary applications based on shape memory alloy (SMA) technology. In order to help realize this goal and reduce the development time and required experience for the fabrication of SMA actuation systems, several modeling tools have been developed for common actuator types and are discussed herein along with case studies, which highlight the capabilities and limitations of these tools. Due to their ability to sustain high stresses and recover large deformations, SMAs have many potential applications as reliable, lightweight, solid-state actuators. Their advantage over classical actuators can also be further improved when the actuator geometry is modified to fit the specific application. In this paper, three common actuator designs are studied: wires, which are lightweight, low-profile, and easily implemented; springs, which offer actuation strokes upwards of 200% at reduced mechanical loads; and torque tubes, which can provide large actuation forces in small volumes and develop a repeatable zero-load actuation response (known as the two-way shape memory effect). The modeling frameworks, which have been implemented in the design tools, are developed for each of these frequently used SMA actuator types. In order to demonstrate the versatility and flexibility of the presented design tools, as well as validate their modeling framework, several design challenges were completed. These case studies include the design and development of an active hinge for the deployment of a solar array or foldable space structure, an adaptive solar array deployment and positioning system, a passive air temperature controller for the regulation of flow temperatures inside of a jet engine, and a redesign of the Corvette active hatch, which allows for pressure equalization of the car interior. For each of the presented case studies, a prototype or proof-of-concept was fabricated and the experimental results and lessons learned are discussed. This analysis presents a collection of CASMART collaborative best practices in order to allow readers to utilize the available design tools and understand their modeling principles. These design tools, which are based on engineering models, can provide first -order optimal designs and are a basic and efficient method for either demonstrating design feasibility or refining design parameters. Although the design and integration of an SMA-based actuation system always requires application- and environment-specific engineering considerations, common modeling tools can significantly reduce the investment required for actuation system development and provide valuable engineering insight.

Near-equiatomic NiTi shape memory alloy (SMA) torsional tube actuators were trained for two-way shape memory effect (TWSME) by repeated thermal cycling under an isobaric load. Performance of the trained actuators was assessed by thermally cycling through a complete phase transformation under a range of isobaric loads that varied from negative to positive and included loads near zero. To assess the actuation performance of the trained SMA components, extended isobaric thermal cycling and cycling under varying loads to constant strain limits was performed. Additionally, isothermal loading was applied in the fully martensitic state prior to and following training. Results show stable TWSME when cycling under significant isobaric loading in the trained direction, however at low or negative loads (loads applied opposite to the training direction) a degradation of TWSME occurred during thermal cycling. Isothermal loading showed that martensite variant reorientation and detwinning was redistributed in the trained actuator when compared to an untrained actuator. Thermal cycling against constant strain limits was shown to have a negligible effect on the stability of the TWSME and overall performance of the trained actuator. Various combinations of isothermal and isobaric loading were shown to expand the operating range at low and negative loads. Additionally, load paths were identified which limit the degradation of TWSME over extended cycling. The aforementioned results are discussed in the context of the correlation between uniaxial isobaric and isothermal loading and texture measurements obtained by in-situ neutron diffraction at stress and temperature. These results show various thermomechanical combinations of heating and loading sequences that yield the same final martensite texture in SMA, which highlights the ability to take different paths yet still obtain the desired actuator response while minimizing irrecoverable deformation mechanisms. The implications of extending these uniaxial results to the design and fabrication and ultimately improving the performance of torsional SMA actuators are discussed.

Shape recovery in shape memory alloys (SMAs) occurs against external stress by means of a reversible thermoelastic solid state phase transformation typically between so-called austenite, martensite and R-phases. The ability to do work enables their use as high-force actuators in automotive and aerospace applications while superelastic NiTi is of interest in biomedical devices such as stents. Both R-phase and martensite can detwin, reorient and undergo a thermal or stress induced transformation. For these reasons, it is difficult from ordinary macroscopic measurements to decouple elastic and inelastic contributions (from their respective phases) from the overall deformation. In situ neutron diffraction is ideally suited to probing these microstructural and micromechanical changes while they occur under external stress fields.