Use Of Shape Memory Alloys Research Articles

MICROSTRUCTURAL AND THERMAL INVESTIGATIONS OF CU-AL-MN-NI SHAPE MEMORY ALLOYS

Abstract Shape memory alloys manifest two distinct characteristics, namely shape memory effect and superelastic effect. They are used in a wide variety of engineering, medical and commercial applications. The use of shape memory alloys in a particular application depends on the shape memory characteristics, viz., shape recovery strain and transformation temperatures. The martensitic transformation and its reversibility form the basis of these functional properties. The transformation temperatures are much influenced by alloying addition, grain-refinement, thermomechanical treatment, etc. In this work, the effect of composition, in general, and that of nickel, in particular, on the microstructure and transformation temperatures and thermodynamic parameters have been explored. The microstructural and phase analyses were carried out by optical microscopy and X-ray diffraction, respectively. The thermodynamic quantities/parameters, such as enthalpy and entropy associated with the transformations as well as the transformation temperatures, were determined by differential scanning calorimetry. The phase analyses were also carried out by thermogravimetry and differential thermal analysis. The results have been analysed and discussed in this paper

Shaping an Origami Shading Device through Visual and Thermal Simulations

This paper presents the first results of a research work aimed at the optimisation of a shading system through parameters of visual comfort – Useful Daylight Illuminance (UDI), Daylight autonomy (DA) and Daylight Glare Probability (DGP) – and Total Energy (TE) consumption (cooling, heating and lighting per year). The goal is to define a shading system for office buildings that delivers visual comfort for users whilst reducing energy consumption for indoor climate control and artificial lighting.As the design of the shading system considers the use of shape memory alloys (SMA) as micro-actuators to accomplish solar adaptation, Origami pattern has been adopted to guarantee a relatively large displacement of the shading system with a small deformation of the SMA wires actuators. Thanks to this shape change, generating overlapped pleats and angle variation and using different materials, it has been possible to provide alterations of the direct light transmission inside the building while maintaining a certain degree of diffuse light component.

Design and testing of a shape memory alloy buoyancy engine for unmanned underwater vehicles

The US Navy’s 2004 Unmanned Underwater Vehicle (UUV) Master Plan outlines the Navy’s aim to expand the role of UUVs, and one of the key areas of interest is the increase in UUV range and endurance. A class of UUVs known as underwater gliders achieves this objective by cyclically modifying its buoyancy and covering horizontal distance with a climb/dive pattern. The present study proposes the use of shape memory alloys (SMAs) in a buoyancy heat engine where the oceanic thermocline would be exploited to produce martensite-austenite phase transformations that in turn change the buoyancy of a piston-cylinder prototype. The working principle of the device involves transitioning between the following two states. At low temperature (at depth) the SMA wires are tensioned into a detwinned martensitic state by a parallel compressed spring. This moves the piston within the cylinder to increase the chamber dry volume and device buoyancy. At higher temperatures (near the surface) the SMA wires undergo a martensite-to-austenite phase transformation, recover part of the applied strain, and reduce the volume and buoyancy of the piston-cylinder. This paper presents the analysis, design, fabrication, and testing of a prototype device. The prototype was immersed in a water bath, and it was demonstrated that its volume would change, as expected, with change in temperature of the water bath. Simulation results showed good correlation with test data.

Machinability analysis when drilling Kovar shape memory alloys

The use of shape memory alloys is noticeably increasing in numerous industrial sectors including aerospace, automotive and marine. This is mainly owing to their intrinsic properties such as expansion-control ability when subjected to thermal loads, large recoverable strain as well as superior mechanical and corrosion resistance properties. Following to producing semi-final parts of shape memory alloys such as bars or sheets, several machining processes are typically employed to generate required features such as holes and slots and to meet dimensional and surface finish requirements. This study aims to investigate the machinability of a shape memory alloy known as Kovar when mechanical drilling using high-speed steel (HSS) twin-lipped twist drills. The influence of cutting speed, feed rate and backup/support conditions is evaluated against process key responses involving cutting temperature, exit burr height and micro-hardness. Additionally, limited qualitative assessment of the machine surface topography and cutting edge was undertaken. Cutting speed was found to be statistically significant affecting the cutting temperature at the 90% confidence level. Dramatic reduction (up to 85%) in exit burr size was obtained when drilling backed workpiece materials compared with the un-backed counterparts.

Design, Manufacturing and Test of a High Lift Secondary Flight Control Surface with Shape Memory Alloy Post-Buckled Precompressed Actuators

The use of morphing components on aerospace structures can greatly increase the versatility of an aircraft. This paper presents the design, manufacturing and testing of a new kind of adaptive airfoil with actuation through Shape Memory Alloys (SMA). The developed adaptive flap system makes use of a novel actuator that employs SMA wires in an antagonistic arrangement with a Post-Buckled Precompressed (PBP) mechanism. SMA actuators are usually used in an antagonistic arrangement or are arranged to move structural components with linearly varying resistance levels similar to springs. Unfortunately, most of this strain energy is spent doing work on the passive structure rather than performing the task at hand, like moving a flight control surface or resisting air loads. A solution is the use of Post-Buckled Precompressed (PBP) actuators that are arranged so that the active elements do not waste energy fighting passive structural stiffnesses. One major problem with PBP actuators is that the low tensile strength of the piezoelectric elements can often result in tensile failure of the actuator on the convex face. A solution to this problem is the use of SMA as actuator material due to their tolerance of tensile stresses. The power consumption to hold deflections is reduced by approximately 20% with the Post-Buckled Precompressed mechanism. Conventional SMAs are essentially non-starters for many classes of aircraft due to the requirement of holding the flight control surfaces in a given position for extremely long times to trim the vehicle. For the reason that PBP actuators balance out air and structural loads, the steady-state load on the SMAs is essentially negligible, when properly designed. Simulations and experiments showed that the SMAPBP actuator shows tip rotations on the order of 45°, which is nearly triple the levels achieved by piezoelectric PBP actuators. The developed SMAPBP actuator was integrated in a NACA0012 airfoil with a flexible skin to carry out wind tunnel tests.

Experimental analyses of dynamical systems involving shape memory alloys

The use of shape memory alloys (SMAs) in dynamical systems has an increasing importance in engineering especially due to their capacity to provide vibration reductions. In this regard, experimental tests are essential in order to show all potentialities of this kind of systems. In this work, SMA springs are incorporated in a dynamical system that consists of a one degree of freedom oscillator connected to a linear spring and a mass, which is also connected to the SMA spring. Two types of springs are investigated defining two distinct systems: a pseudoelastic and a shape memory system. The characterisation of the springs is evaluated by considering differential calorimetry scanning tests and also force-displacement tests at different temperatures. Free and forced vibration experiments are made in order to investigate the dynamical behaviour of the systems. For both systems, it is observed the capability of changing the equilibrium position due to phase transformations leading to hysteretic behaviour, or due to temperature changes which also induce phase transformations and therefore, change in stiffness. Both situations are investigated by promoting temperature changes and also pre-tension of the springs. This article shows several experimental tests that allow one to obtain a general comprehension of the dynamical behaviour of SMA systems. Results show the general thermo-mechanical behaviour of SMA dynamical systems and the obtained conclusions can be applied in distinct situations as in rotor-bearing systems.

Kinetic Solar Skin: A Responsive Folding Technique

The paper focuses on optimized movements analysed by means of Origami, the Japanese traditional art of paper folding. The study is a way to achieve different deployable shading systems categorized by a series of parameters that describe the strengths and weaknesses of each tessellation. Through the kinetic behaviour of Origami geometriesthe research compares simple folding diagrams with the purpose to understand the deployment at global scale and thus the potential of kinetic patterns’ morphology for application in adaptive facades. The possibilities of using a responsive folding technique to develop a kinetic surface that can change its configuration are here examined through the variation of parameters that influence kinematics’ form. Moreover, in order to perform the shape change without any external mechanical devices, the use of Shape Memory Alloy (SMA) actuators has been tested.

UNCERTAINTY ANALYSIS OF A ONE-DIMENSIONAL CONSTITUTIVE MODEL FOR SHAPE MEMORY ALLOY THERMOMECHANICAL DESCRIPTION

The use of shape memory alloys (SMAs) in engineering applications has increased the interest of the accuracy analysis of their thermomechanical description. This work presents an uncertainty analysis related to experimental tensile tests conducted with shape memory alloy wires. Experimental data are compared with numerical simulations obtained from a constitutive model with internal constraints employed to describe the thermomechanical behavior of SMAs. The idea is to evaluate if the numerical simulations are within the uncertainty range of the experimental data. Parametric analysis is also developed showing the most sensitive constitutive parameters that contribute to the uncertainty. This analysis provides the contribution of each parameter establishing the accuracy of the constitutive equations.

Hand neuro-rehabilitation system using Nitinol spring actuators

This paper presents the design and implementation of a neuro-rehabilitation system for hands based on Nitinol actuators. The design process of a mechanism to assist hand rehabilitation therapies of spastic patients is presented. The system is based on the use of shape memory alloy (SMA) springs, Nitinol mainly, as the actuation system, being that this system presents compliance behavior that is needed for these rehabilitation therapies. The design described uses this actuation system to perform hand rehabilitation therapies, recommended by a physiotherapist. The software developed for programming and supervising the therapies is also presented. The results obtained when using the system in a patient with right hemiparesis are shown.

An accurate, fast and stable material model for shape memory alloys

Shape memory alloys possess several features that make them interesting for industrial applications. However, due to their complex and thermo-mechanically coupled behavior, direct use of shape memory alloys in engineering construction is problematic. There is thus a demand for tools to achieve realistic, predictive simulations that are numerically robust when computing complex, coupled load states, are fast enough to calculate geometries of industrial interest, and yield realistic and reliable results without the use of fitting curves. In this paper a new and numerically fast material model for shape memory alloys is presented. It is based solely on energetic quantities, which thus creates a quite universal approach. In the beginning, a short derivation is given before it is demonstrated how this model can be easily calibrated by means of tension tests. Then, several examples of engineering applications under mechanical and thermal loads are presented to demonstrate the numerical stability and high computation speed of the model.

Design, characterization and perspectives of shape memory alloy elements in miniature sensor proof of concept

The use of shape memory alloys (SMAs) has found numerous applications in several different areas. In particular, in the mini/micro actuation field, SMAs have the advantage of having high power to weight ratio, improved reliability and reduced complexity in the design of the active mechanism. In recent years, several devices have been developed that use SMAs to promote free recovery (null forces), constrained recovery (partial displacement) or work-producing devices. In all these cases, forces and/or displacements are produced by the SMA element upon a heating/cooling cycle.This paper presents an experimental investigation on the potentiality of using SMA in the development of self-contained temperature sensors. The current work proposes some proof of concept devices based on both the one-way and the two-way shape memory effect exhibited by the same NiTiCu alloy wire. The results of the thermal and mechanical characterizations of the SMA element are reported. The choice of the shape of the SMA element, core of the sensor activation, and of the configuration of the whole device are presented in different variations for the one-way and two-way configurations. Finally, a functional investigation of the assembled sensors illustrates their features in terms of operating temperature and cycling effect. The proposed design concepts confirms the effectiveness of SMA in the light-weight technology and they show some examples of sensor applications in miniature scale that can be calibrated in terms of operating temperature, overall dimensions and SMA strain-to-output transducing method.

Airfoil morphing based on SMA actuation technology

Purpose – This study aims to develop an innovative actuator for improving the performance of future aircraft, by adapting the airfoil shape according to the flight conditions. The flap’s camber of a civil regional transportation aircraft’s trailing edge actuated and morphed with the use of shape memory alloys (SMA) actuator technology, instead of the conventional split flap mechanism is studied. Design/methodology/approach – For the flap’s members sizing an efficient methodology is utilised based on finite element (FE) stress analysis combined to analytically formulated design criteria. A mechanical simulation within an FE approach simulated the performance of the moving rib, integrating both aerodynamic loads and SMA phenomenology, implementing Lagouda’s constitutive model. Aim of this numerical simulation is to provide guidelines for further development of the flap. A three-dimensional assembly of the flap is constructed to produce manufacturing drawing and to ensure that during its morphing no interfer...

SU‐C‐19A‐02: An Innovative Critical Organ Repositioner Device for Use During Radiotherapy Treatments

Purpose:In most radiation oncology applications the use of shape memory alloy (SMA) actuation can be extremely beneficial in sparing normal structures by relocating them away from the path of the external beam, or placing distance between the structure and radiation source such as in Brachytherapy. Implementation of this organ repositioner device in conjunction with IMRT could open new possibilities for dose escalation and significant dose reduction to normal tissues. Similarly, in high dose rate brachytherapy applications, the ideal effective dose may not be delivered to the target volume due to toxicity concerns to adjacent critical structures. Here we present a dual functioning device manufactured from SMA materials to: 1) provide a desirable tool to reposition the organ at risk away from the radiation source, and 2) facilitate localization when imaging the area.Methods:A Nitinol based actuator with controlled force and displacement will be incorporated in the design of an organ repositioner (e.g., a rectal marker) with the ability to recall a pre‐defined shape at temperature T1 (body temp) and shift back to its original shape at temperature T2 (to facilitate removal). An open distal end permits the marker to function as a part of a barium delivery system.Results:An example of this SMA manufactured in our laboratory for atrial fibrillation radio frequency ablation is the esophagus SMA positioner, designed to position the esophagus away from the ablation area. This device shows the maximum strain in the deflected esophagus to be less than 3%. The prototype positioner deflected the organ at risk by 5 cm away from the site of ablation.Conclusions:The organ repositioner device is feasible for use in clinics, provides patient comfort due to its gradual deflection, and has dual functionality in repositioning the organ at risk as well as serving as a localization device.

Beam balancing ball driven by shape memory alloy: prospective actuator for stabilised control

An alternative actuation mechanism is applied to the most sought after control laboratory system - the ball on beam. The system is driven by antagonistic shape memory alloy (SMA) wires which are engaged to play the role of both sensing and actuation in closed loop. The control objective is to govern the position of the ball on the beam. The angular altitude of the beam is varied by shifting the lateral position of the beam, through control of the smart actuator's angular acceleration. The focus is to study the use of SMA for systems with complex dynamics. A discrete sliding mode controller is implemented which requires no detailed information about the constitutive model of SMA. The differential resistance of the antagonistic SMA wires measured during actuation is utilized as the sensing signal. The innovation in this work is direct feedback of the measured signal which is facilitated by a specially designed signal processing electronics. The performance of the self-sensing under actuated system is illustrated through real time position control.

Experimental investigation of the influence of the heating rate in an SMA actuator performance

The use of shape memory alloys (SMAs) as actuators has an increasing importance in several areas. In general, the shape memory effect and the two-way shape memory effect are employed in order to produce displacements and/or forces by heating the SMA actuator above the phase transformation temperature. This paper presents an experimental investigation on the heating rate influence on an SMA actuator. Basically, an experimental apparatus is built by considering NiTi wire connected to a steel spring and monitored by sensors. The heating rate varies from 2.9°C/min to 385°C/min by applying an electrical current in the SMA actuator. Several situations are investigated highlighting the general thermomechanical behavior associated with the influence of heating rate.

Density dependence of the superelastic behavior of porous shape memory alloys: Representative Volume Element and scaling relation approaches

As the use of Shape Memory Alloys (SMAs) grows increasingly common in many industrial applications, the porous form of SMA is of particular interest as it associates both the shape memory effect and superelasticity with the characteristics of foam. However, numerical prediction of the mechanical response of SMA foam is very challenging due to the micro–macro nature exhibited by the material, as the porous microstructure is several orders of magnitude smaller than the overall dimensions of the macroscopic porous sample. To circumvent, or at least alleviate this computational weight, an attempt is made to describe the superelastic behavior of SMA foams using two approaches: Representative Volume Element (RVE) and scaling relation; the latter is based on modeling the fully-dense material with mechanical properties equivalent to those of its porous counterpart. This approach avoids direct modeling of the porous microstructure and thus contributes to a drastic reduction of the computational cost. A validation is made by comparing the numerical results obtained in this study with experimental results taken from the literature.

Review on Biomechanical Simulation, Measurement and Control of Orthodontic Force

The forces and moments supplied by braces determine the movement of tooth in orthodontic treatment, so clearly quantifying the force value is very important to formulate precise treatment plan. In recent decades, scholars have presented many articles about biomechanical research on orthodontic force. Based on investigations of these papers, techniques on orthodontic force stimulation including oral model (bone, PDL and teeth included) reconstruction and constitute model construction, methods in orthodontic force measurement including physical oral model fabrication and device architectures, and techniques on orthodontic force control such as the use of shape memory alloy and shape memory polymer as the wire material, are reviewed. At the end, the conclusions and future works are given.

Removed at authors request

The forces and moments supplied by braces determine the movement of tooth in orthodontic treatment, so clearly quantifying the force value is very important to formulate precise treatment plan. In recent decades, scholars have presented many articles about biomechanical research on orthodontic force. Based on investigations of these papers, techniques on orthodontic force stimulation including oral model (bone, PDL and teeth included) reconstruction and constitute model construction, methods in orthodontic force measurement including physical oral model fabrication and device architectures, and techniques on orthodontic force control such as the use of shape memory alloy and shape memory polymer as the wire material, are reviewed. At the end, the conclusions and future works are given.

Modeling of rate-dependent damping capacity of one-dimensional superelastic shape memory alloys

Recent experimental tests showed that shape memory alloys have a strong dependence of stress–strain curve on the strain rate. This rate-dependent phenomenon is mainly due to the temperature variation of shape memory alloys caused by the latent heat release/absorption during the forward/reverse phase transformation. Since there is an increasing use of shape memory alloys for civil engineering like seismic application, the complex rate-dependent properties, such as the propagation stress and the damping capacity, should be carefully analyzed. This article studies the rate-dependent stress–strain curve, especially the damping capacity, of one-dimensional NiTi shape memory alloys by using a linear model and a nonlinear model taken the rate-independent driving force in the micromechanics-inspired constitutive model. Compared with the experimental data and previous work, both models use fewer material parameters and can easily describe the trend of damping capacity with respect to the strain rate. For their clear physical meaning and simple mathematical expression, both models are useful tools for the dynamic design and simulation of superelastic shape memory alloys in practice.

Analyzing mechanical properties and nondestructive characteristics of brazed joints of NiTi shape memory alloys to carbon steel rods

Research is being conducted on the use of shape memory alloys, in particular NiTi, in civil engineering, due to the superelastic behavior of NiTi which can be used for damping. In this particular application, NiTi has to be joined to steel, which constitutes a major difficulty due to the considerably different properties of materials involved and the poor weldability of NiTi. Brazing was investigated for this application, since it is an economic and efficient process to joint dissimilar materials. This paper presents a study on the mechanical behavior in the superelastic regime of dissimilar NiTi/steel joints and the feasibility of a nondestructive method based on eddy currents to characterize the weld metal. Brazed joints in lap configuration were produced with a 20 % Ag braze alloy and tested under fatigue conditions in the superelastic regime. Lap joints of steel rods to NiTi ribbons have undergone up to 60 cycles of load/unload without rupture at a maximum load of the superelastic plateau close to the pull-out load of the joint. Measurements of the electrical impedance, with a helicoidal cylindrical coil along the lap joint, allowed the identification of the location of the joint, with a good spatial resolution characterizing the morphology of the brazed joints.