The generation and variation of forces necessary to achieve a training stimulus is often realized in sports and rehabilitation equipment by manually adjustable masses or by complex motor-brake systems. This leads to heavy and unwieldy systems, which cannot be used flexibly, and in addition to high costs. The main objective of this paper is to prove that pseudoelastic shape memory alloys (SMA) are potentially suitable for use in sports and rehabilitation equipment and offer additional value in the area of training flexibility combined with high training resistance. Therefore, the properties of pseudoelastic SMAs for this application were investigated. These multifunctional materials offer the potential for special elastic and sensory properties. The pseudoelastic effect is based on stress-induced martensite formation, which allows high elastic deformations. During this phase transformation, the mechanical stress passes through a plateau. The stress plateau can be moved by changing the temperature of the SMA. The determination of properties of pseudoelastic SMAs with different alloy compositions was carried out according to the specifications of “VDI 2248: Product Development with Shape Memory Technology”. With a functional model based on the material tests, which replaces a commercially available force clamping device, the monitoring of force, displacement and temperature changes can be realized by the integrated sensor technology. This paper presents the methodology, experiments and findings for the use of pseudoelastic SMAs in sport and rehabilitation devices. It concludes with prospects to commercial application.

This paper presents the modeling, simulation and wind tunnel experimental verification of the aeroelastic behavior of a two-degree-of-freedom (pitch and plunge) typical airfoil section with superelastic shape memory alloy helical springs in the pitch degree-of-freedom. A linearly elastic spring is considered in the plunge degree-of-freedom. Although viscous damping is considered in both degrees-of-freedom, hysteretic damping simultaneously takes place in the pitch degree-of-freedom due to the (stress-induced) pseudoelastic behavior of the shape memory alloy springs. The shape memory alloy phase transformation kinetics and constitutive modeling are based on Brinsons model and the shape memory alloy helical spring behavior is based on classical spring design. The nonlinear effects of shape memory alloy phase transformation are included in the shape memory alloy spring modeling for the representation of hysteretic force-displacement behavior. A two-state linear aerodynamic model is employed to determine the unsteady pitching moment and lift. The aeroelastic behavior of the typical section is numerically and experimentally investigated for different preload levels applied to the shape memory alloys. Numerical predictions and experimental results show that for large enough preload levels (such that shape memory alloy phase transformations take place at small pitch angles) unstable post-flutter regime is replaced by stable limit-cycle oscillations. Moreover, the amplitudes of aeroelastic oscillations decrease with increasing preload levels since more expressive phase transformations are achieved at small pitch angles. Although the amplitudes of the post-flutter limit-cycle oscillations increase with increasing airflow speed (since aerodynamic loads increase with the square of the airflow speed), they remain bounded within acceptable levels over a range of airflow speeds due to hysteretic damping. Moreover, the cutoff airflow speed increases with increasing preload. The experimentally verified results show that the pseudoelastic behavior of shape memory alloy elements can passively enhance the aeroelastic behavior of a typical section.

Shape setting is a fundamental step in the production route of Nitinol Shape Memory Alloys (SMAs) for the fixing of the functional properties, such as the shape memory effect and the pseudo-elasticity. The conventional method for making the shape setting needs the use of furnaces. In this work laser technology was adopted for performing the straight shape setting on commercially available Nitinol thin wires. The laser beam was moved along the wire length for inducing the functional performances. Calorimetric and pseudo-elastic response of the wires, laser annealed, were studied; high energy X-Rays diffraction was done for studying the evolution of the microstructure texture. It can be stated that the laser technology can realize the shape setting of thin SMA wires with pseudo-elastic properties; the wire performances can be modulated in function of the laser power.

Shape Memory Alloys (SMAs) are active metallic materials classified as “smart” or “intelligent” materials along with piezoelectric ceramic and polymers, electro-active plastics, electro-rheological and magneto-rheological fluids and others. SMAs show a multitude of different and dependent properties interesting for technological applications. These properties depend on the peculiar deformation mechanisms, accounting for the so-called shape memory effect. SMAs are nowadays used in quite different fields, like thermo-mechanical devices, anti-loosening systems, biomedical applications, mechanical damping systems, in some cases employed for large scale civil engineering structures. These multifunctional materials can be naturally considered as sensor-actuator elements demonstrating large possibilities for applications in high-tech smart systems. The use of SMAs in actuators offers an excellent technological opportunity to develop reliable, robust, simple and lightweight elements within structures or as stand-alone components that can represent an alternative to electro-magnetic actuators commonly used in several fields of industrial applications, such as automotive, appliances, consumer electronics and aerospace. NiTi-based SMAs demonstrated to have the best combination of properties, especially in terms of the amount of work output per material volume and the large amount of recoverable stress and strain. However, there are several limiting factors to a widespread diffusion of SMAs to technological fields. For instance, SMAs display a critical dependence of the shape-memory related properties, like transition temperatures, on their actual composition. For this reason, a great care in the production steps, mainly based on casting processes, is required. Another critical aspect, that is to be considered when dealing with SMAs, is the strong influence of their thermo-mechanical history on their properties. This may disclose interesting perspectives of application to smart devices in which different aspects of the shape memory phenomenology, like one and two way shape memory effect, pseudoelasticity, damping capacity, etc., are used. Last, but not least, one of the most debated aspects around NiTi alloys is microcleanliness. This concept is becoming increasingly important as the industrial market moves to smaller, lower profile devices with thinner structures. In this work a general overview about the peculiar behavior of NiTi alloys along with their main issues, the shape memory components under development, and the main efforts and directions for materials improvement will be presented and discussed. A bird’s-eye view on the future opportunities of NiTi-based shape memory actuators for industrial applications will also be given.

A Shock and vibration isolator is widely used due to its simplicity and effectiveness. It attenuates vibration energy when the external excitation frequency is more than about 2 times its natural frequency, while the vibration around its natural frequency is generally amplified. However, an exciting frequency often varies so that it is difficult to avoid the vibration amplification. In particular, when these amplification phenomena occur in the low frequency domain, induced large vibration displacements degrade the structural integrity. This paper introduces a novel frequency tunable isolator proposed by the present authors. The isolator uses SMA wires as actuator as well as the isolation materials. The isolator material is a compressed mesh washer isolator using the pseudoelasticity of SMA. Frequency tune of the isolator can be easily achieved through a simple electric circuit. Thus, this isolator can be widely applied to various vibration and shock environments such as in aircrafts and motor vehicles. Particularly, the detail design procedure is presented here for the adaptive shock isolator for launch vehicle in order to achieve both shock attenuation performance and avoidance of the vibration amplification. Launch vehicles experience severe dynamic environment during the flight phase. Specially, pyroshock generated from the several separation events could result in malfunctions of electric components and low frequency vibration below 100 Hz at the maximum dynamic pressure phase could reduce the structural integrity of payload. The resonant frequency of the isolator is selectively controlled in two modes by using an adaptive mechanical system with compressing the isolation materials. The isolator was successfully designed and various test results with frequency tuning are presented, in this paper.

Processing of Nickel-Titanium (NiTi) shape memory alloys (SMAs) is challenging because smallest compositional variances and all types of microstructural features strongly affect the elementary processes of the martensitic transformation and thus the functional properties of the material. Against this background, powder metallurgical near net shape methods are attractive for the production of NiTi components. Especially additive manufacturing technologies (AM) seem to provide high potential, although they have received only little attention for processing NiTi so far. This work is the first to report on pseudoelastic properties of additive manufactured Ni-rich NiTi. We show how to establish pseudoelasticity in NiTi samples prepared by the additive manufacturing technique Selective Laser Melting (SLM). Therefore, we analyze phase transformation behavior, mechanical characteristics and functional properties of our materials subjected to different heat treatments. The obtained results are compared to the behavior of conventional NiTi. The presented results clearly indicate that SLM provides a promising processing route for the fabrication of high quality NiTi parts.

Shape memory alloys (SMA) are well-known for their ability to transform into an imprinted shape by means of thermal activation (pseudoplasticity) or after a mechanical deformation (pseudoelasticity). The thermal effects can be used in a wide range of industrial applications like valves, unlocking devices or comfort applications in the field of automotive mechatronics. While there are many ideas concerning shape memory actuators, only few thoughts have been spent on service applications around these unique actuators. At present, product-related services are usually considered as an add-on to the actual product. But in future, industrialized countries are subject to a structural change toward service societies. For this reason, new concepts and methods which enable the companies to design the potential services in an optimal way are necessary already during the development of a product. This is a paradigm shift from the separated consideration of products and services to a new product understanding consisting of integrated products and services. In the case of shape memory technology, recycling processes present an interesting field for such integrated services. Starting with general ideas towards recycling concepts for and with shape memory components, this paper focuses on refresh-annealing as an example of an interesting recycling process. Finally, the paper is summed up by an outlook on future works on development methods for generic shape memory actuators and their service systems. The aim of this study is to show the possibilities and the importance of services in the field of shape memory technology. As a result, new applications and markets for SMA can be developed.

Shape memory alloys such as Nitinol, which is a group of NiTi alloys composed of nearly equiatomic nickel and titanium, finds increasing applications in many industries because of its unique properties including the shape memory effect and pseudoelasticity. In past work simple linear actuators have been developed using Nitinol wire which are actuated and controlled using resistive heating. However, traditional Nitinol materials are batch processed and a monolithic component only possesses a single set of transformation temperatures, limiting the functionality of the actuator. In this work a linear actuator processed using the novel multiple memory material processing technology is presented showing multiple transformations and dynamic actuation by resistive heating. This dynamically controlled actuation greatly improves the functionality of the Nitinol actuator allowing for the realization of new applications and improved control methods. The different transformation temperatures embedded in the monolithic wire actuator following processing are identified using thermo-analytical analysis and the dynamic application of load and displacement are presented using a custom test set-up.

Temperature changes caused by latent transformation heats are an integral part of the behavior of shape memory alloys and inevitably couple the thermal and the mechanical fields. This general behavior is covered by the Mu¨ller-Achenbach-Seelecke (MAS) model. Its versatility has been documented extensively in the literature. In the original formulation the MAS model is restricted to uniaxial states of stress in a SMA, which limits its application to cases where such stress states prevail, such as axial loading in wires and trusses, as well as pure beam bending, pure torsion and shrink-fit problems. Unreliable results, however are expected under arbitrary multiaxial loading conditions. To overcome this limitation we present an extension of the model capable of arbitrary stress/strain/temperature states in 3D. Our model adopts ideas presented by Xie but employs a different non-convex free energy function. Rate equations are employed to model temperature or stress/strain induced transformations between austenite and eight variants of martensite present in the model. As the MAS model, the multi-variant model is capable of fully-coupled thermo-mechanical processes which is shown by simulations of temperature-induced processes, quasiplasticity and pseudoelasticity under variable load directions. At the present level of sophistication, the model is restricted to single crystalline SMA. All examples are explained by the use of a standalone model implementation. The model is intended for future implementation into the finite-element-method environment ABAQUS™ to provide a powerful tool useful in the framework of engineering design studies, especially in situations which require non-isothermal conditions and phase transitions.