Papers by Keyword: Shape Memory Alloy Actuator

Abstract: low pumps have been developed for classical applications in Engineering and medicine. They are vital instruments in areas such as Biology where the applications demand many such devices in miniaturized form to handle life saving fluids and drugs. The aim of this paper is to develop a new bio-mimic fluid pump, designed to achieve miniaturization in its size and volume. A new actuation technique is proposed which pumps the fluid based on the principle of flow due to pressure difference created by varying the cross-section of a flexible tube. The novelty and advantage being, no external pressurizing device is needed and the flow can be made bidirectional. This is in general not possible in normal or traditional pumps. Use of SMA wires as actuators helps in keeping the size and weight of the device as low as possible. The working principle of the device and the conceptual design are discussed. Mathematical model, relating the flow parameters required for controlling the device, and analytical results obtained from such relations are presented.

Abstract: Nowadays Shape Memory Alloys (SMAs) are used as actuators in many applications such as aerospace structures. In sandwich structures, the SMA wires or plates are used in the skins for shape control of the structure or vibration damping. In this paper, bending behavior of sandwich plates with embedded SMA wires in their skins is studied. 3D finite element method is used for construction and analysis of the sandwich plate with a flexible core and two stiff skins. Some important points such as continuity conditions of the displacements, satisfaction of interlaminar transverse shear stresses, the conditions of zero transverse shear stresses on the upper and lower surfaces and in-plane and transverse flexibility of soft core are considered for accurate modeling and analysis of sandwich structures. Solution for bending analysis of sandwich plates under various transverse loads are presented and the effect of many parameters such as plate dimensions, loading conditions, material properties of core, skins and SMA wires are studied. Comparison of the present results in special case with those of the three-dimensional theory of elasticity and some plate theories confirms the accuracy of the proposed model.

Abstract: This paper demonstrates, theoretically and experimentally, the feasibility of utilizing Shape Memory Alloy (SMA) as an actuator in controlling the flexural vibrations of a flexible cantilevered beam. The shape memory alloy used in this study is merely a straight wire which is made of nickel titanium alloy called Nitinol. Acting as tendons, these SMAs undergo phase transformation, to the austenitic phase, producing significant forces and displacement capabilities as well as low power consumption. This actuator unit is composed of a SMA wire attached to a spring in series. After being set-up with a load cell the transfer functions of the actuator are measured. Considering the uncertainty of the actuator unit performance the H-infinity optimal controllers are designed and installed into the control system. By integrating the thermal and dynamic characteristics of the SMA into beam dynamical model the composite beam-actuators system can now be developed. The robust stability performance of the designed controller is evaluated through vibrational test on the cantilever and the result is shown to be adequately attenuated.

Abstract: This paper presents a fan clutch driven by SMA spring actuator. Based on shape memory effect of SMA, the operational principle of the fan clutch driven by SMA is introduced. The equation of the output displacement of SMA actuator in free stroke is derived. The normal pressure between driving and driven discs of the clutch generated by SMA actuators is analyzed to compute the torque transmission ability in the disc-type fan clutch. The characteristic of transmission torque is studied in detail. The results indicate that the change of temperatures has a tremendous influence on the normal pressure between driving and driven discs of the fan clutch, and the transmission torque of the fan clutch changes rapidly according to the temperatures of airflow from radiator.

Abstract: Intelligent materials have been studied in various fields. In this study, Shape Memory Composite (SMC) is produced as one of those intelligent materials. SMC consists of Shape Memory Polymer (SMP) and Shape Memory Alloy (SMA). These two materials possess different characteristics in temperature changes. Therefore, we investigated the possibility of the SMC’s actuator function as an intelligent material. The actuator function is achieved by applying a current to SMA fiber of SMC to grab and release objects. As a result of this investigation, meaningful data for actuator to design SMC is obtained.

Abstract: This paper provides an original experimental characterization of the shakedown state of a shape memory alloy structure under cyclic pseudo-elastic loading. This analysis is performed through the observation of the dissipated energy at a macroscopic scale as well as the temperature on the surface of the sample through infrared thermography measurement. Morevover, a deeper study is led thanks to acoustic emission to quantify the shifts between microscopic evolutions at a lower scale. The main conclusion is that these 3 quantities are correlated and enable us to identify different stages the structure crosses until the shakedown state.

Abstract: Shape memory alloy (SMA) reinforced composites have been widely used in aerospace engineering fields. In this paper, four basic assumptions were presented to simply the research model based on the Eshelby’s equivalent inclusion method and Mori-Tanaka scheme. Based on the three-phase equivalent system and two-step equivalent process, the effective elastic modulus and thermal expansion coefficient of unidirectional random distribution short SMA fiber reinforced composites were derived. The tensile mechanical properties of composites with fiber volume fraction (15%), size (L=3, D=1; L=5, D=1), and number (N= 30, 50), were simulated using software ANSYS12.0, and discussed the failure mode of the composites.

Abstract: Ni-Mn-Ga magnetic shape memory alloys are employed for applications in actuators and sensing devices. Ni-Mn-Ga single crystalline alloys exhibit ferromagnetic shape memory effect with large reproducible strains in moderate magnetic fields. The cost for producing single crystals is high and there is a requirement to investigate the polycrystalline Ni-Mn-Ga alloys for similar applications. This work presents a study of the effect of composition and heat treatment on the microstructure, in polycrystalline off-stoichiometric compositions of high Ni, Ni-Mn-Ga alloys. Cast polycrystalline alloys were homogenized and analysed using optical microscopy, X-ray diffraction, and thermal analysis. Stability of the martensitic transformation temperature was studied by aging the alloys at different temperatures. Martensitic structure was found in both the alloys (~ 54at% and 58 at%). The alloy with high Ni~58 at% content was found to be having a dual phase structure (martensite and FCC γ). Single phase Ni-Mn-Ga alloy has shown transformation at temperature >400K while the dual phase alloy with Ni ~58at% has transformed at temperature >700K thus making it suitable for high temperature applications. Martensitic stabilization effect was observed in alloy with Ni ~54 at% after aging treatment while it was absent in alloy with ~58at% Ni.

Abstract: Various heat treatment conditions with temperature scans of 300-700 °C, and annealing time scans of 1-4 hours were adopted in the annealing of Ti-49.5at.%-Ni shape memory alloy ultra thin wires. The mechanical hysteretic curves and the crystal morphology were obtained by the tensile-recovery testing and scan electric microscopes (SEM). The result shows that the shape memory effect of Ni-Ti alloy first decline after rising with the heat treatment temperature increases. Alloy with heat treatment effect in 500°C, presents the best. Time is not a significant factor for heat treatment.

Abstract: Based on thermodynamic theory, a phenomenological model of shape memory alloy is provided. Simulations under different loading illustrate the influence of large-strain deformation and small-strain deformation on the characteristics of the model. The results indicate that the difference between the two methods is small under uniaxial tension case, while the influence is very large under shear deformation case.