Papers by Keyword: Shape Memory Alloy Actuator

Abstract: This paper presents an innovative mechanical actuator using a shape memory alloy (SMA) with a cooling system based on combined thermoelectric effect and forced air cooling systems. The main advantages of using SMAs include the reduction of the system weight, the ease and reliability in application, and a simple control strategy. This study focuses on the development of the system highlighting the mathematical model of the actuator, and an experimental prototype was implemented. Several experiments are used to validate the model and to identify best SMA actuator configuration parameters. Experiments were used to evaluate the actuator closed-loop performance, stability, and robustness properties.

Abstract: The present work summarises the results, which were obtained from studies carried out on the structure of the nitride and nitride-oxide surface layers with use of the electron transmission microscopy. The layers were formed using glow discharge technique at relatively low temperature (300°C). It has been shown that low temperature nitriding or nitriding/oxiding process produced a thin layer ~30 nm thick. They were formed from titanium nitride as well as titanium oxides. The structure revealed that nanoparticles were surrounded by high amount of amorphous phase. Especially, electron microscopy was useful method for studying the phase boundary between the layer and the NiTi matrix. During deposition process, which was carried out at temperature above 300°C, the intermediate layer of Ni3Ti intermetallic phase appeared between titanium oxides and/or nitrides. Lowering deposition temperature down to 300°C or below resulted in absence of such sublayer. Moreover, thickness, structure of layers, absence of sublayer formed during glow discharge process, can significantly influence deformation during inducing of the shape memory or superelasticity effect.

Abstract: Presented work summarizes studies done on the course of the martensitic transformation in the Ti50Ni25Cu25 alloy. Studies were carried out using scanning electron microscopy JEM 6480 equipped with an electron back scattered detector (EBSD) as well as a heating attachment. As-received ribbon was mainly amorphous. At the free side of the ribbon some fine randomly oriented crystalline grains were formed. During heating followed by cooling the reversible martensitic transformation occurred with sequence: B2↔B19. The crystallographic correlation between the B2 phase and the B19 martensite were confirmed. It allowed finding transformation matrix between both phases.

Abstract: The TiNiV shape memory alloy wire that was cold pressed under 9Mpa at the room temperature had good superelasticity. On this basis, a tensile test was made after a series of medium-temperature treatment. Then the effect of superelasticity and microstructure of TiNiV shape memory alloy by medium-temperature treatment were studied. The results indicate that the experimental wires assume thorough non-linear superelasticity after holding 30 min at 430°C. The superelasticity of the wire enhances firstly, then declines with the ascent of the temperature and extension of the time of the holding. A kind of potentiation phase-Ti3Ni4 precipites out of the wire under different medium-temperature treatment.

Abstract: The thermal cycling (quenching in liquid nitrogen and reverting back to room temperature: austenite martensite reversible transformation) response of Ni-Ti-Fe shape memory alloys has been investigated. It was clearly noted that residual deformation, estimated in terms of noticeable differences in austenite grain size, depend on the relative clustering of fine grains. During repeated thermal cycling, the residual deformation, in-grain misorientation developments and retained martensite content scaled together: bringing out a clear picture of microstructural irreversibility.

Abstract: The Nickel-Titanium (Ni-Ti) alloys are the most attractive amongst shape memory alloys (SMA) due to their good functional properties coupled with high strength and good ductility. The transformation temperatures in Ni-Ti SMA can be altered by chemical composition and thermal and/or mechanical treatments adequate to obtain reversible martensitic transformation in one or more steps. The goal of the present work is to investigate the evolution of texture in Ni-Rich Ni-Ti (50.8at%Ni-Ti) SMA showing different phase transformation temperatures as a result of different thermal/mechanical history: straight-annealed (as-received condition) and subsequent thermal treatment at 500°C for 30 minutes in air. The microstructural and textural results were obtained by Electron Backscattering Diffraction on Scanning Electronic Microscopy (ESBD/SEM) and by X Ray Diffraction (XRD) at room temperature. Mechanical properties were measured by Vickers micro hardness tests at room temperature.

Abstract: NiTi based shape memory alloys (SMAs) have been identified as potential candidates for sensors and actuators in various industrial applications. During service life of actuators, SMAs are subjected to large number of stress/strain cycles through the complete transformation range, known as thermomechanical cycling (TMC), which introduces various defects in the material. In the present study, an attempt has been made to understand the microstructural changes taking place during thermo-mechanical cycling of NiTi wires using Transmission Electron Microscope (TEM). These microstructural observations have been discussed in conjunction with the cyclic shape memory behavior of the wires.

Abstract: In this paper a phase transformation equation is supposed to describe the phase transformation behaviors of the shape memory alloy (SMA) under complex stress state. The stress field near crack-tip of mode I in SMA at various temperatures is investigated based on the supposed phase transformation equation and linear elastic fracture mechanics. Results show both the martensite region and the mixed region of martensite and austenite near the crack-tip become larger with the decrease of temperature. The fracture mechanics behaviors of SMA are much influenced by the temperature.

Abstract: NiTi shape memory alloy is widely used in dental applications such as orthodontics arch wire, mini screw implant, orthodontics spring, etc., because of its favorable superelasticity and shape memory effect. Wire drawing is a fundamental manufacturing process used for producing orthodontics arch wires. It is well known that cold-work occurred during wire drawing operation is also important to control mechanical properties and transformation temperature of NiTi wires. Thus, the purpose of this work is to study the effect of cold working by means of reduction ratio of cross -sectional area and heat-treatment temperatures on transformation and mechanical behavior of the drawn wires for utilized as orthodontic wires. The wire material used in this study is Ni51.4Ti48.6 (at%) alloy with various initial diameters with targeted wire diameter of 0.51mm (0.02 inch). The die for wire drawing is made of tungsten carbide which is inserted into a steel case. The dies were designed to have different reduction ratio of cross sectional area for 4 levels; 10%, 20%, 30% and 40%, respectively. The lubricant used in this study is sodium stearate powder. In order to investigate the influences of heat-treatment temperatures, the drawn wires are heat-treated at 400 °C and 600 °C for 3.6ks. The results showed that percentages of reduction of cross sectional area and heat-treatment temperature strongly affect mechanical properties and transformation temperatures. Superelasticity was confirmed in an alloy heat-treated at 400 °C. The results obtained can be used to determine the optimum properties of NiTi wire in order to utilized as orthodontics arch wires.

Abstract: For ductile beam-to-column connectiosn in steel frame, beam local buckling is difficult and very costly to repair in any post-disaster reconstruction. Shape memory alloys (SMAs) in their austenite states have the ability to recover their original shape after experiencing large deformations. Steel connections retrofitted using SMAs can be endowed with intelligent characteristics. This paper investigates extended end-plate connections using long shank SMA bolts. The SMA connection is designed using a new methodology of avoiding beam local buckling and adopting the strong end-plate. The connection deformations are supposed to concentrate on the SMA bolts. In order to study the seismic behaviour of the connections, quasi-static tests were conducted on both the SMA connection specimens. The test results indicate that the connection can show high deformation capacity with the maximum interstory drift angles beyond 0.02 rad. However, the beam was remained elastic during test and the deformations of the SMA connection were recoverable upon unloading. The load-drift hysteresis loops are flag-shaped for the SMA connection. This indicates that the connection has moderate energy dissipating capacity.