Advances in Science and Technology Vol. 78

Abstract: We present the simulation and development of a vibration energy harvester based on an active element made of Ni-Mn-Ga Magnetic Shape Memory (MSM) alloy. As the MSM element is subjected to mechanical stress within an external magnetic field, its magnetization changes in proportion to its length, facilitating energy generation in a pick-up coil. Whereas conventional piezo and magnetostrictive devices operate with small (sub-millimeter) stroke at high frequencies (kHz range), the MSM harvester is best suited to longer (millimeter range) stroke at a low frequency (100 Hz or below). Power output of 20 mW has been demonstrated with the prototype device operating at 45 Hz.

Abstract: Shape Memory Alloys (SMAs) exhibit complex behaviors as a result of their constituent phases and microstructure evolution. In this paper, we focus on the numerical simulations of microstructure evolution in SMAs using a phase-field model for the two dimensional square-to-rectangular martensitic phase transformations. The phase-field model, based on the Ginzburg-Landau theory, has strong non-linearity, thermo-mechanical coupling, and higher-order differential terms and presents substantial challenges for numerical simulations. The isogeometric analysis, developed in this paper using the rich NURBS basis functions, offers several advantages in solving such complex problems with higher-order partial differential equations as the problem at hand. To our best knowledge, we report here for the first time the use of the new method in the study of microstructure evolution in SMAs. The numerical experiments of microstructure evolution have been carried out on the FePd SMA specimen. The results are in good agreement with those previously reported in the literature.

Abstract: It is well-known that the Ti-Ni shape memory alloy (SMA) is applicable to the medical stent. The repeated heat-treatment under the constrained strain is necessary for the manufacturing process of the laser-cut SMA stent. In this research, the effect of heat-treatment under the constrained strain on mechanical properties of the Ti-Ni shape memory alloy wire was investigated. The applied strain at single heat-treatment (εap) was 4, 5 and 8%, and the heat-treatment is repeated so as to became total applied strain 40%. In the case of εap=4 and 5%, partial transformation occurs in the SMA wire, and so a necking appears in the SMA wire. Due to this necking, multi-step martensitic transformation, and decreasing of breaking strength / breaking strain are caused. The necking does not occur because the whole of the SMA wire is transformed for εap=8%. The mechanical properties are improved by increasing of εap. Nevertheless, the mechanical properties of each sample are inappropriate for the medical stent. However, the mechanical properties of the as-manufactured sample are improved greatly by training. In addition, it is desirable that the applied strain during training is slightly larger than the requested strain for application.

Abstract: Pseudoelastic NiTi-based devices are often required to recover their shape repeatedly and their working performance can be judged from the amount of residual deformation after use. The quality problem in this respect can even be removed from fatigue life or safety issues and impact on the functional and aesthetic value of the product. While linear deformation can be appreciated quantitatively in a straightforward manner, the bending strains are more difficult to assess directly. We devised a very simple digital image-based method to measure the residual bending deformation by comparison of the pristine shape of the device with the one resulting from bending and free recovery. The program was written in LabView and is capable of reporting about the deflection and location of strain concentration along slender pseudoelastic elements in a semi-quantitative way appropriate for quality sample checks. The method is semi-automatic and provides a user-friendly interface for the operator. Apart from simple shapes like straight wires and ribbons, the method was tested on devices as complex as spectacles frames. This application is particularly interesting, where shape recovery and functional and aesthetic value are tightly linked, and deformation by severe handling is a typical effect of use.

Abstract: We have found that deposited film can be crystallized without the post-annealing treatment but with the simultaneous ion-irradiation during sputter-deposition at very low substrate temperature. The present paper reviews the low temperature crystallized TiNi films deposited by the above technique. An RF magnetron sputtering apparatus equipped with separate confocal sources as well as with a heating and ion-irradiating system for substrates was used to make the films crystalline. Without using the ion-irradiating system, the films deposited on ambient-temperature substrate have been amorphous. However, crystallized film is deposited even at 353 K of substrate temperature with using the system. Appropriate ion-irradiation is considered to be help to crystallize the film at low substrate temperature. Broad and doublet X-ray diffraction profile of the film, which was diffracted from B19’ and/or R phase, was recorded between 42 degree to 45 degree in 2 theta. The crystallized film deposited on a polyimide sheet was cut into the shape of a double-beam cantilever and the ends of the two beams were connected to an electrical power supply. The cantilever shows a repeatable two-way motion by electrical cycle of 0.1 Hz at room temperature.

Abstract: TiNi is well known as a typical shape-memory alloy, and is expected to be a promising material for micro actuators. In order to realize micro electro mechanical systems (MEMS) with this material, we have to get thin crystal film of the material, since the shape-memory property appears only when the structure is crystalline. In our previous studies we developed a new apparatus as well as a new deposition process for lowering the crystallization temperature by using ion irradiation. In addition, we have found that the deposited film by the process can be crystallized at very low temperature (below 473 K) without annealing but with simultaneous irradiation of Ar ions during sputter-deposition. In this study, we aim for the realization of crystallized TiNi film, which is deposited on Si substrate below 373 K substrate temperature. In order to realization the purpose, we have revealed the effect of Ar ion energy on lowering the crystallization temperature. The ion energy is measured with a quadrupole mass spectrometer (QMS) having an ion energy analyzer. The deposited TiNi films are examined with an X-ray diffraction (XRD). We found the plasma potential against the reactor chamber is important to be considered in the ion irradiation energy. The effects of ion energy for the crystallization of TiNi film are discussed.

Abstract: Several solutions have been proposed to mitigate the vibrations of stay cables in bridges, which are subjected to wind, rain and traffic loads. One possible solution relates to the use of semi-active devices, such as the ones based on magneto-rheologic fluids. These devices need guaranteed electrical power, together with computational effort and technical attention. In contrast, shape memory alloy (SMA) wires were studied for application as passive elements. In the present work, the properties of SMA that are required to realize dampers provided with an appropriate reliability are discussed. In particular, the fatigue/fracture life of the SMA wires and the thermal effects induced by both external temperature and the self-heating process are studied. The SMA dampers were applied to stayed cables of realistic size and tested in "facilities." Namely, the cables No 1 of 45 m length available at the ELSA-JRC in Ispra, Italy, and the 50 m cable of IFSTTAR near Nantes, in France, were considered. The experimental results establish a reduction of the vibration amplitude to one half or less than the one observed in the un-damped case. Furthermore, the installation of the SMA dampers causes an increase of the cable frequency. Performing a Windowed Fourier Transform or a Wavelet Transform analysis the evolution of frequency with the signal amplitude was studied. The change of amplitude produces a change of stiffness in the SMA. The adoption of an appropriate phenomenological model of the hysteresis cycle permits to perform numerical simulations using standard Finite Elements Analysis tools such as, for instance, the ANSYS software.

Abstract: Recent research is showing that Shape Memory Alloys (SMA) can be advantageously employed for a number of applications in Rehabilitation Medicine and the related field of Neuroscience. This innovative use of SMA was investigated with the specific aim of improving the treatment approach to neurological patients with sequelae from stroke, traumatic brain injury, cerebral palsy, etc. Several examples of devices built for this purpose will be presented together with an outline of the reasons why the shape-memory and pseudoelastic effects can be regarded as interesting resources on account of scientific, technical and clinical reasons. In particular the design and functioning of an SMA-based ankle exerciser and pseudoelastic repositioning splints for the upper and lower limbs will be discussed in relation with results of neurophysiologic and clinical tests. The main observations so far suggest that this type of devices is able to support patients’ physical rehabilitation by adapting to changing conditions and needs during functional recovery. Furthermore, due to their improved tolerability relative to traditional treatments SMA devices can be used for longer times and tend to produce interesting effects in the control of spastic syndromes.

Abstract: Machine tools for small work pieces are characterized by an extensive disproportion between workspace and cross section. This is mainly caused by limitations in the miniaturization of drives and guidance elements. Due to their high specific workloads and relatively small spatial requirements, Thermal Shape-Memory-Alloys (SMA) possess an outstanding potential to serve as miniaturized drives in small machines. However, most of the known SMA drive applications necessitate additional guidance elements to realize a certain mechanical stiffness. In this paper we present a novel SMA actuator design, which does rather not require an additional guidance. The stiffness in directions different from the actuators moving direction is realized by a specific arrangement of the SMA elements. Those are designed regarding geometry, applied load, and control aspects. Furthermore, a sample actuator is built to investigate the capabilities to serve as miniaturized feed axis in small machines.

Abstract: Magnetic shape memory alloys (MSMA) offer remarkable potentials for actuation purposes because of a large achievable strain and a short response time. But, apart from these advantages, MSMA show a hysteretic behavior between the input and output quantities. Hysteretic phenomena represent an important challenge for the design of control systems for MSMA-based actuators. Furthermore, this hysteretic behavior is sensitive to temperature variations, a situation that arises in many applications. To face the problem of increasing/decreasing temperature during operation, an open-loop control approach considering temperature variations is presented in this paper. For this purpose, an actuator prototype is characterized with particular emphasis on temperature influence concerning the input-output behavior. The presence of a time-varying nonlinearity is addressed by means of a set of hysteresis models and relative compensators to improve the positioning performance of the actuator system. Subsequently, the obtained models are integrated in the control loop and tested experimentally. Finally, the results achieved with the introduced control concept are presented.