Shape memory alloys (SMAs) are a novel solution to reducing the actuating system weight and mechanical complexities which consequentially comes with integration challenges. Some of these challenges are due to limited production accessibility and often need reengineering. A materials model turned into analytical routines would allow empirical data to predict the structural behavior of SMAs. An SMA design tool would bridge material science and engineering practices by guiding the users through an iterative design approach to improve integration efficiency for actuating devices. A user-friendly first-order approximation model was developed by the Consortium for the Advancement of Shape Memory Alloy Research and Technology (CASMART) to capture the macroscopic effects of forward and reverse transformation for various actuator types such as wires, springs, and torque tubes. This tool allows quick changes and iterations throughout the design process, which is particularly helpful in comparing actuator types. Although it is convenient to use, the ability to capture the SMA nonlinear and complex inelastic response is limited. Phenomenological-based models have been developed by incorporating classical theory of plasticity and by relating martensite volume fraction to the laws of thermodynamics. The phase transformation can be characterized as a rate-independent plasticity using the volume of martensite to govern the change in material properties between austenite and martensite. The development of the model itself incorporates other characteristics such as the degradation of performance due to plastic strain and the change in transformation strain during partial cycling. The challenge with these models is the complexity for the user. The starting point to create a user-friendly SMA design tool involved combining a phenomenological-based model with Finite Element Models (FEM). Integrating a complex 3D constitutive model with ABAQUS Finite Element Analysis (FEA) encompasses both conventional material parameters and unique shape memory alloy parameters.

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.

Solar concentrators increase the amount of usable energy available in solar collection systems by focusing energy through an aperture to which energy is magnified within the area of its trajectory. Design challenges of a solar concentrators for space applications are to make them more lightweight, compact, and exhibit a smooth and consistent reflective surface curvature for optimal performance. Shape memory alloys (SMAs) offer an effective and compact solution to engineering needs, such as solar reflectors, to reduce weight and improve overall energy collection and concentration performance. The one-way shape memory effect can be used for this application, where the SMA is heat treated in a strained designed curvature by forcing the austenite microstructure to “remember” the original shape even after deformation. SMAs are capable of actuating from the stow configuration and into the designed shape after the solar energy exposure induces a phase transformation. In this study, NiTi and NiTiCu SMAs were thermomechanically processed into plates and cut into three sizes of triangular chips for use as reflector components. Standard binary NiTi SMAs was modified with the substitution of Cu for Ni to achieve a narrower hysteresis and better thermomechanical cycling stability. The SMAs were produced from commercially available NiTi SM495 plates by ATI Specialty Alloys and Components (Albany, OR) and custom-melted NiTiCu buttons. Each processing step was comprehensively characterized to monitor microstructural and thermomechanical property changes using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and Vickers hardness (HV). The NiTi and NiTiCu triangular chips were shape-set utilizing a custom-made apparatus to attain the intended curved surface with specific dimensions for a reflector component within a solar concentrator.

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.

In this work, a new method of processing shape memory alloys was utilized to understand the effects of disrupting the martensitic long range order and forming amorphous nanodomains with martensitic short range order. Based on the obtained results, strain glass alloy states were analyzed and confirmed using various characterization methods to determine trends and compare two alloys, Ni 49.5 Ti 50.5 and Ni 50.8 Ti 49.2 . For Ni 49.5 Ti 50.5 a 33% thickness reduction was required to obtain a cold work-induced strain glass state, while for Ni 50.8 Ti 49.2 a 24% reduction was required.

Typical processing techniques involve thermo-mechanically treating the material such as cold working and subsequent annealing to control grain and precipitate size, shape, orientation, and morphology. Shape memory alloy (SMA) mechanical properties rely heavily on microstructural features such as precipitates and grain size to extend fatigue life. Novel approaches to control microstructural features have used laser anneal on amorphous NiTi thin films to recrystallize grains and short-time annealing on NiTi after angular extrusion and cold-drawn fine wires. A recent study examined rapid thermal annealing (RTA) on Ni-lean NiTi- 10 at.% Hf wires as an effective method for controlling grain size and extending actuation fatigue; however, flash annealing or RTA on Ni-rich NiTiHf high-temperature SMA (HTMSA) wires has not been investigated. Based on a larger study, Ni-rich NiTi-20 at.% Hf HTSMA was down-selected for further processing. This study investigates the effect of flash annealing on the thermo-mechanical properties of a Ni-rich Ni50.3Ti29.7Hf20 HTSMA. Microstructural changes were examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Actuation fatigue properties were also evaluated at 300 MPa. The results indicate that flash annealing HTSMA wires is an effective method for controlling grain size and extending fatigue life. The heating rate and time held are crucial parameters to control microstructural features such as grain size and coherency.